Franklin-Wistar Friction Machine?

 

 

The Leyden jars are partially filled with shavings of cast iron. No visible oxide on the surface of the grains. Two point contacts, one milimeter appart on the surface of a grain, produce less than 10 ohms of series resistance. The smaller, long neck Leyden jar has two electrodes made-out of iron. One terminates with a nice spherical head and the other shows some left over fiber probably used to tide-up there some whiskers. The leyden jars can be set up close to the glass cylinder during charging and the "afflux or efflux of electrical fire" estimated. Furthermore, the pine wooden plank on which the experiment is set has three unused holes which may indicate that the wood was used previously for something else. I speculate that the contraption is not a commercial machine or a kit but a research apparatus made by people versed in glass blowing under specification of a scientist studding the "electrical fire".

 

The two pictures above shows how the silk or fur was held on the cylinder. Most glass, through friction, charges positively. The electrons dissipate in air through the carefully shaped steel wire holder. Initially I thought that the maker of this machine avoided deliberately any metallic parts, even nails, except in the Leyden jars and the holder of the rubbing material. This was not true; in the middle of 18 century, nails and screws were not yet popular fasteners. The bottle for the Leyden jars were held, in the last stage of manufacturing, with a fused glass bar on the bottom. That permitted the glass blower to achieve a well rounded opening. At the right four bottles attributed to Gaspar Wistar are shown. Although most of the bottles manufactured in this era are similar, I speculate that the Leyden jars on our electrostatic machine are made with Wistar bottles. Recently in the article "Buttons to Bottles" the author writes:."Wistar glass also enjoys the historic and scientific honour of having been made to specification for Benjamin Franklin, who incorporated Wistar glass in a variety of devices he designed for his experiments in electricity. Franklin tested his first lightning rod at Caspar Wistar’s house".

 

Please see three portable friction machines bellow. The first one was presented as belonging to Ben Franklin.

To me, the machines in the last rows are commercial versions of a research friction machine as in NSM collection: the Franklin-Wistar machine. The only improvement are the pins on the wheels that permit a more forceful rubbing and what was learned from Frankin experiments: the comb which "will effuse electric fire" (provide neutralization charge for the positively charged glass cylinder and in the process will charge the Leyden jar).

The one below here, I photographed at Harvard collection; it is cataloged as "English-made, circa 1800, with 19th century repairs".

An almost identical machine, attributed to Thomas Corbett (1780-1857), Canterbury, N.H., and dated 1810 is pictured bellow. One have to look for details to observe that indeed the three machine are not three pictures of the same.

Cast iron (I hope I remember well) has a lower melting point if the carbon content is higher. Probably, first iron shafts were machined out of high carbon content cast iron. In the picture above is the content of the Leyden jars associated with our electrostatic machine. The neck of the smaller leyden jar shows the marks left by the forming tool. "punty" marks on the bottom.

"punti" mark can be observed on the base of the large jar, where a rod was attached during the blowing process.