526 PHILOSOPHICAL TRANSACTIONS. [aNNO 1754. 



The description of Professor Richman's apparatus, as sent by himself to Pro- 

 fessor Heinsius of Leipsic, he called an electrical gnomon. To the construction 

 of this gnomon were necessary a rod of metal, a glass jar, a linen thread of a 

 foot and half in length, to one end of which was fastened half a grain of lead, 

 and a quadrant. The rod of metal' cd, fig. 3, pi. 11, was placed in the glass 

 vessel E, which contained filings of metal. The linen thread cg was fastened to 

 the rod at c, and, when the apparatus is not electrized, hangs perpendicularly 

 down. The radius of the quadrant, which was divided into degrees, was 2 lines 

 more than a foot and half in length. And here must be added an account of 

 the other part of the apparatus, which was to communicate the electricity to the 

 gnomon during a thunder storm. Through a glass bottle, the bottom of which 

 was perforated, passed an iron rod, which was kept in its place by means of a 

 cork fitted to the mouth of this bottle, through which cork likewise was inserted 

 the iron rod. A tile was removed from the top of the house ; and on this open- 

 ing was placed the bottle, supported by the neighbouring tiles, in such manner 

 that one end of the iron rod was not only 4 or 5 feet above the top of the house; 

 but the other end, which came through the bottom of the bottle, did no where 

 touch the tiles, or any other part of the house. To this end of the iron rod was 

 fastened an iron chain, which was conducted into the chamber of Professor 

 Richman, on electrics per se, so as no where to touch the building. The en- 

 trance to this chamber faced the north ; and at the south end of it there was a 

 window, near which stood a table 4 feet in height. On this the Professor placed 

 his electrical gnomon, and connected it with the chain, which was brought under 

 the ceiling of the room over this table, and communicated with the apparatus on 

 the top of the house, by means of a wire bc, which hung from the chain, and 

 was joined there to ab, by the little ring b, and communicated with the rod do 

 at c. When the iron rod at the top of the house was affected by the thunder, 

 or othei-wise suitable condition of the atmosphere, the thread before- mentioned 

 deviated from the perpendicular; as it would also do, if artificially electrized. 

 The Professor always observed a greater ascent of the thread from artificial elec- 

 tricity than by that from the atmosphere. By the former, he had seen it on the 

 quadrant describe an angle of above 55", but never above 30 by the latter. In 

 the year 1752, Aug. Q, the apparatus acquired so great a degree of electricity 

 from the atmosphere, that from the end of the rod the electrical flashes might 

 be heard at several feet distance. Under these circumstances, if any one touched 

 the apparatus, they felt a sharp stroke in their hand and arm. 



Professor Richman sometimes added to this apparatus a glass bottle of water, 

 after the manner of Professor Muschenbroek hi, adapted to a vessel of metal ik, 

 olaced on glass. The wire from the mouth of the bottle of water hl, during 

 ihe time of the thunder, he caused to communicate with bc. From this addi- 



