The Thompson Improved Steam Indicator comes in a dark stained wooden box 285mm wide, 207mm deep, and 240mm tall. It opens about halfway up its height to reveal a number of objects. The box, as well as various components, are serial numbered 4994. Inside the box there are pockets as well as mounts for the various objects to go into which can be seen in the images provided.
In the center is the steam indicator, which resembles two off-center attached cylinders screwed onto a mount. The cylinders are both 90mm in height and 50mm in diameter. The top cylinder has a slot to affix a cardstock, a stylus arm and pull string. The bottom cylinder has the arm holding the stylus and a spring inside to control the stylus arm. The bottom of the bottom cylinder has threads and ties to the mount on the bottom of the box, as well as thumb bars on the bottom to attach or unattach it by hand.
The steam indicator comes with 6 springs numbered 10, 20, 30, 40, 60, and 80, which range in length from 53-63mm long. These springs are threaded onto mounts on the upper half of the box and can replace the spring inside the bottom cylinder of the steam indicator. This allows the system to make more precise graphs depending on the pressure that the engine is putting out.
In addition to the above, there are also two globe shut-off valves with thread sizes of 20 and 25mm. The valves come with caps for one side to prevent damage to the threads that could result in inadequate attachment . There is also a torque wrench used to tighten the lower cylinder onto the engine that the indicator will be attached to. There is also a small vial of oil, for the joints of the stylus arm or the springs. There was also a specialized wrench designed to tighten the components in order to prevent gas leaks. The final component was a ruler with a screw driver end that allowed for the dismantling of the indicator as well as measuring the height of the graphs drawn by the arm allowing the user to find the pressure in the system.
Functional Description:
In order to use the Thompson steam indicator, the user fastened the stainless-steel ball valve to the steam engine being analyzed. The indicator was then be fastened to the open end of the ball valve via a threaded connection. With the ball valve opened, the steam within the engine’s piston exerts pressure on a spring enclosed within a 100 mm tall, 30 mm diam. cylinder of the indicator. A plunger connected to the spring is forced upward depending upon the force received by the spring. The motion of the plunger moves the 80 mm long arm vertically, which determines the markings made by the attached pencil. The pencil marks a piece of paper, which is wrapped around the upper cylinder (90 mm tall and 51 mm dia) of the indicator. Wrapped around this upper cylinder is a string whose function is to rotate the cylinder about its center. If the string were left free to hang, the steam pressure pushes the pencil upward, making a straight vertical line on the paper. However, the string was fastened to a component of the engine to allow for the engine piston and the cylinder to move in unison. The string moves the cylinder of the steam indicator in unison with the piston throughout the entire stroke, and a continuous marking is made to illustrate the pressure at each point of the stroke as the pencil is moved upward and downward while the cylinder pivots throughout the process. Thus, the vertical motion of the pencil graphs changes in pressure, while the rotation of the cylinder indicates the phase of the piston cycle, and so in unison the pencil plots a diagram of the pressure cycle in the engine.
The indicator was designed to record the stroke of a steam engine, particularly locomotives. At the start of the stroke, the inlet valve opens completely, allowing the maximum force to be applied to the spring by the steam. The pencil marks a horizontal line at its highest point in the cycle from left to right. At cut-off, the inlet valve closes and expansion of the steam occurs, during which the force gradually decreases. This phase is indicated by a pencil mark resembling an exponential decay curve. At release, the exhaust valve opens, releasing the steam and the force is at its minimum, resulting in a straight horizontal pencil mark at the lowest point of the curve—this time from right to left. When the exhaust valve closes, compression occurs, causing a gradual rise in pressure. When the inlet valve opens again, the gradual increase in pressure becomes a sharp increase, causing the pencil to mark a straight vertical line returning to the first point of the cycle when the steam pressure exerts its greatest force on the spring. The end product of this device is a card illustrating the change in pressure throughout the continuous cycle of the steam engine. For an engine operating at 250 RPM, the device could generate one cycle plot (or card) per minute.
The spring within the indicator can be replaced with a larger spring to record higher steam engine pressures. The set of springs are marked according to their compressive strength: the spring marked #100 converts the force from 100 psi gauge-pressuresteam into a pencil movement of one inch, a #80 spring converts 80 psig steam into a movement of one inch, and so on.
Though the steam indicator was primarily used on locomotives, it could also be applied to traction engines and artillery. Due to the high cost of the indicator, it was seldom used on traction engines beyond the confines of the factory in which it was produced. When applied to heavy artillery, the oil in the recoil chamber would replace the steam as the working fluid and exert a pressure on the spring. The string would be fastened to the barrel to allow for the recoil movement to pull on the string.
]]>The Thompson Improved Steam Indicator comes in a dark stained wooden box 285mm wide, 207mm deep, and 240mm tall. It opens about halfway up its height to reveal a number of objects. The box, as well as various components, are serial numbered 4994. Inside the box there are pockets as well as mounts for the various objects to go into which can be seen in the images provided.
In the center is the steam indicator, which resembles two off-center attached cylinders screwed onto a mount. The cylinders are both 90mm in height and 50mm in diameter. The top cylinder has a slot to affix a cardstock, a stylus arm and pull string. The bottom cylinder has the arm holding the stylus and a spring inside to control the stylus arm. The bottom of the bottom cylinder has threads and ties to the mount on the bottom of the box, as well as thumb bars on the bottom to attach or unattach it by hand.
The steam indicator comes with 6 springs numbered 10, 20, 30, 40, 60, and 80, which range in length from 53-63mm long. These springs are threaded onto mounts on the upper half of the box and can replace the spring inside the bottom cylinder of the steam indicator. This allows the system to make more precise graphs depending on the pressure that the engine is putting out.
In addition to the above, there are also two globe shut-off valves with thread sizes of 20 and 25mm. The valves come with caps for one side to prevent damage to the threads that could result in inadequate attachment . There is also a torque wrench used to tighten the lower cylinder onto the engine that the indicator will be attached to. There is also a small vial of oil, for the joints of the stylus arm or the springs. There was also a specialized wrench designed to tighten the components in order to prevent gas leaks. The final component was a ruler with a screw driver end that allowed for the dismantling of the indicator as well as measuring the height of the graphs drawn by the arm allowing the user to find the pressure in the system.
Functional Description:
In order to use the Thompson steam indicator, the user fastened the stainless-steel ball valve to the steam engine being analyzed. The indicator was then be fastened to the open end of the ball valve via a threaded connection. With the ball valve opened, the steam within the engine’s piston exerts pressure on a spring enclosed within a 100 mm tall, 30 mm diam. cylinder of the indicator. A plunger connected to the spring is forced upward depending upon the force received by the spring. The motion of the plunger moves the 80 mm long arm vertically, which determines the markings made by the attached pencil. The pencil marks a piece of paper, which is wrapped around the upper cylinder (90 mm tall and 51 mm dia) of the indicator. Wrapped around this upper cylinder is a string whose function is to rotate the cylinder about its center. If the string were left free to hang, the steam pressure pushes the pencil upward, making a straight vertical line on the paper. However, the string was fastened to a component of the engine to allow for the engine piston and the cylinder to move in unison. The string moves the cylinder of the steam indicator in unison with the piston throughout the entire stroke, and a continuous marking is made to illustrate the pressure at each point of the stroke as the pencil is moved upward and downward while the cylinder pivots throughout the process. Thus, the vertical motion of the pencil graphs changes in pressure, while the rotation of the cylinder indicates the phase of the piston cycle, and so in unison the pencil plots a diagram of the pressure cycle in the engine.
The indicator was designed to record the stroke of a steam engine, particularly locomotives. At the start of the stroke, the inlet valve opens completely, allowing the maximum force to be applied to the spring by the steam. The pencil marks a horizontal line at its highest point in the cycle from left to right. At cut-off, the inlet valve closes and expansion of the steam occurs, during which the force gradually decreases. This phase is indicated by a pencil mark resembling an exponential decay curve. At release, the exhaust valve opens, releasing the steam and the force is at its minimum, resulting in a straight horizontal pencil mark at the lowest point of the curve—this time from right to left. When the exhaust valve closes, compression occurs, causing a gradual rise in pressure. When the inlet valve opens again, the gradual increase in pressure becomes a sharp increase, causing the pencil to mark a straight vertical line returning to the first point of the cycle when the steam pressure exerts its greatest force on the spring. The end product of this device is a card illustrating the change in pressure throughout the continuous cycle of the steam engine. For an engine operating at 250 RPM, the device could generate one cycle plot (or card) per minute.
The spring within the indicator can be replaced with a larger spring to record higher steam engine pressures. The set of springs are marked according to their compressive strength: the spring marked #100 converts the force from 100 psi gauge-pressuresteam into a pencil movement of one inch, a #80 spring converts 80 psig steam into a movement of one inch, and so on.
Though the steam indicator was primarily used on locomotives, it could also be applied to traction engines and artillery. Due to the high cost of the indicator, it was seldom used on traction engines beyond the confines of the factory in which it was produced. When applied to heavy artillery, the oil in the recoil chamber would replace the steam as the working fluid and exert a pressure on the spring. The string would be fastened to the barrel to allow for the recoil movement to pull on the string.
The object was made by the firm the American Steam Gauge Company of Boston, MA. The indicator was initially invented by James Watt, who also is credited with the invention of the steam engine. Joseph Thompson is the creator of this steam engine indicator with his patent being granted on Aug 31, 1875. The instrument was manufactured by The American Steam Gauge Company, which was founded in 1851. The instrument was sold as the “American Thompson Improved Indicator”, and was considered to be high end among steam indicators of the time. The improvements of the Thompson indicator over previous models were that the writing component followed an elliptical pattern to maintain a straight line on the recording barrel. This resulted in less inertia and increased the engine speeds, and pressures that the indicator could be used at. The patent granted in 1904 to Earl Vaughn had the benefits of making the indicator easier to disassemble for adaptability of the indicator. For this reason it is believed that this indicator was manufactured sometime after 1904.
"The Story of the Steam Engine Indicator." last modified July/August 2001 http://www.farmcollector.com/steam-traction/story-steam-engine-indicator
Engineer: with which is incorporated steam engineering, volume 35 .. Vol. 42. (Chicago: The Engineer Publishing Company, 1905).
Dorn, Harold. Dictionary of Scientific Biography. Vol. 14. (New York: Charles Scribner's Sons, 1976), 196-99.
Physical description: A nickeled brass surveyor's cross in a wooden fitted case. The cross consists of a cylinder with a compass on the top and a gimbaled socket on the bottom for mounting on a stake or tripod.
The main body of the instrument consists of a cylinder of two parts, the upper of which has two pairs of slits set at 90˚ to one another. The lower section has one pair of slits directly opposite each other (i.e., 180˚ apart). Each pair has two types of slits, the "eyepiece slit" which is a beveled slot with two beveled circular pinholes at either end (and thus looks like an elongated barbell), and the "objective slit", which is wider with a fine sighting wire strung vertically through it. Both slits are 30mm tall with the eyepiece slit <1mm side, and the objective slit about 4mm wide strung with <1mm diam. wire.
There is a meridional band engraved where the top and bottom cylinders meet. The top edge of the lower cylinder is marked in 360˚ by single degrees and the lower edge of the upper cylinder has a Vernier scale marked 0–60' by 2' whose zero sligns with one eyepiece slit above. The second perpendicular set of slits sights 90˚ to the right from this principle set of slits.
On the bottom of the cylinder are two 20mm diam. knurled knobs. One is geared within to allow the upper section of the cylinder to be rotated minutely and the other locks the rotation.
Functional description: The surveyor's cross is used to set a perpendicular to a given line during surveying, although this more advanced pantometer can sight a second line at a prceise angle to the baseline. One uses either the upper or lower eyehole depending on whether the bearing of the line descends or ascends from the current station, since the opposed slits can only be used in one direction each. Having set the top cylinder to zero on the 360˚ meridonal scale, the surveyor may either sight a given line of an existing survey and read off its compass bearing (this instrument therefore acting like a simple surveying compass) or set the instrument from a written survey description that includes a compass bearing. In this case one can use the lower sight to set a line, rotate the top cylinder a set amount, and then sight a second line and its perpendicular. Alternatley, by zeroing the cyllinders and sighting on one line with the bottom slits, the top cylinder can be rotated to another line and the angle between read off the meridonal band to 2' of arc.
The typical method of use for a simple cross would be for the surveyor to take a tripod out to a known survey point and then set the bearing of one of the slits (choosing the one pair so that the other pair sight either left or right as will be needed). Then by locking the head in place and sighting though the other slit, the surveyor's assistant ('rodman') can move as far away as desired and then adjust laterally until he is on the perfectly perpendicular line.
Further information: Gillespie 1901, 59-60; Schmidt 2007.
This particular form of a surveyor's cross was named a "Goniasmomètre" (Fr.) or "goniometer" (Engl.; literally meaning simply "an angle-measurer"), and seems to have been primarily favored in France (Gillespie, 1901, 200, no. 304). It is properly known as a "pantometer", an instrument for measuring all angles, and as a "Equerre d'arpenteur" (lit., a "surveyor's bracket"). In its most general form of a cylinder with slits, it goes back to the seventeenth century, but its dual-cylinder Vernier form seems to have been developed for military surveying about the first third of the nineteenth century, perhaps by a Mssr. Fouquier, of the École Polytechnique (Laisné 1839, 61).
According to the label inside the storage case, this instrument was awarded a gold medal at the Brussels’ 1888 "Grand Concours: international des sciences et de l'industrie," part of the World's Fair there in that year. This relatively small expo is quite understudied, having been eclipsed the very next year by the Exposition Universelle in Paris (for which the Eiffel Tower was built). The pantometer was also awarded a “Diplome d’Honneur’ at the Exposition Internationale d'Anvers in Antwerp in 1894. The unknown maker apparently exhibited at 7 major European fairs (but no American ones) between 1851 and 1894, suggesting that this is likely a major and known maker.
The label and ink stamp in the case from two major expositions suggests that it was the type of instrument (or even just surveying instruments by this maker) that received the award, not this specific object. In many cases the actual prize-winning object would have its medal mounted in or on the case as well. The fact that the paper label has a pasted in label from an 1888 exposition and then a inked stamp from 1894 suggests that this particular instrument was made sometime between the two. Further research in the exhibitor catalogs for these exhibitions would be fruitful. [1]
It is interesting that there is no indication of the maker anywhere on the cross, or even on the labels, but this seems to be a not-uncommon feature of the type of instrument: see similar and contemporaneous examples at the Harvard collection here and here (without a compass), and here from the Smithsonian; and a comparable early twentieth-century one here. There are similar pantometers known by instrument makers Salmoiraghi of Milan, H. Bretschneider of Halle, Stanely in London, and even after WWI by SLOM in Paris.
By comparison, a simple surveyor's cross (presumably without a Vernier) could be had from Gurley (1889, 304) for only $3 or $6 with a compass on top. They also sold a complex version "with vertical axis and divided circle, to take angles" for $12.
This example was purchased in 1984 at the monthly antiques market in Brussels by Bob Carnanan (MTU Class of 1953). Received by MTU Social Sciences and IHSI, July 31, 2019.
Notes
[1] A preliminary check of the 1894 Antwerp foreign exhibitors in Class 8, "Objets scientifiques, cartographie, etc." (EUd'A 1894, 276-278) suggestst that this will be harder to figure out than not. Of the 42 exhibitors from France, only two Parisienne firms are listed as potentially showing surveying instrumetns (Alfred Berthélemy showing "Instruments de précision, optiqiue, mathémathique, géodésie, nivellement, [et] topographie" and Vion Bros. of Paris, exhibiting "Instruments d'géodésie"), but numerous others are listed showing generic "precision instruments" or "instruments for the sciences." Specific items shown are not listed.
Nicolàs de Hilster, "Geodetic Instruments: Surveyor's crosses: Pantometer," n.d. [online].
Exposition Universelle d'Anvers [EUd'A], Catalogue officiel général. II, Sections étrangères (Bruxelles: A. Mertens, 1894).
William Mitchell Gillespie, A Treatise on Surveying: Comprising the Theory and the Practice (New York: D. Appleton, 1901).
Joseph Laisné, Aide-mémoire portatif à l'usage des officiers du génie (Burssels: Meline, Cans et Compagnie, 1839).
Wilhelm A. Schmidt, "Second Thoughts: The Surveyor's Cross," Professional Surveyor Magazine 27, no. 3 (March 2007) [online]