TRANSACTIONS OP THE SECTIONS. l*J 



and with acid of the same strength, but the arrangement in which the pairs were 

 isolated in a Wedgewood trough, liberated three or four times tbe amount of gases 

 in the voltameter, as the arrangement on Martyn Roberts' plan. The battery, when 

 arranged as the author proposes, will be one compact mass, which can be readily 

 moved in and out of the cells ; this will probably more than compensate for the loss 

 by the action of the acid on the iron surface not exposed to the zinc, as the battery 

 need only be kept in the acid when actually at work ; and this loss may perhaps be 

 further prevented by covering the outside of the iron with a resinous mixture ; but 

 should the cast-iron cell suggested by Callan be preferred, they can be easily cast with 

 the addition required in this arrangement. As cast-iron plates 5 inches square can 

 be procured for 2d. each at any foundry, and no binding screws are required, this 

 battery will probably be found much cheaper and quite as efficient as any published, 

 and especially adapted for experimentalists who make their own apparatus, who will 

 know how to appreciate the cheap and easy method for making the connexions. A 

 more detailed account, with an engraving of this battery, may be seen in the 

 ' Chemist ' for November 1856. 



On Dellman's Method of observing Atmospheric Electricity. By 

 Professor William Thomson, M.A., F.R.S., Glasgow. 



Extract from letter addressed to General Sabine : — " During my recent visit to 

 Creuznach I became acquainted with Mr. Dellman of that place, who makes meteoro- 

 logical, chiefly electrical, observations for the Pnassian Government, and I had oppor- 

 tunities of witnessing his method of electrical observation . It consists in using a copper 

 ball about 6 inches diameter, to carry away an electrical effect from a position about 

 two yards above the roof of his house, depending simply on the atmospheric ' poten- 

 tial ' at the point to which the centre of the ball is sent ; and it is exactly the method 

 of the ' carrier ball ' by which Faraday investigated the atmospheric potential in the 

 neighbourhood of a rubbed stick of shell-lac, and other electrified bodies (' Experi- 

 mental Researches,' Series XI. 1837) . The whole process only differs from Faraday's 

 in not employing the carrier ball directly, as the repeller in a Coulomb-electrometer, 

 but putting it into communication with the conductor of a separate electrometer of 

 peculiar construction. The collecting part of the apparatus is so simple and easily 

 managed that an amateur could, for a few shillings, set one up on his own house, if 

 at all suitable as regards roof and windows ; and, if provided with a suitable electro- 

 meter, could make observations in atmospheric electricity with as much ease as ther- 

 mometric or barometric observations. The electrometer used by Mr. Dellman is of 

 his own construction (described in Poggendorff's 'Annalen,' 1853, vol. Ixxxix., also 

 vol. Ixxxv.), and it appears to be very satisfactory in its operation. It is, I believe, 

 essentially more accurate and sensitive than Peltier's, and it has a great advantage in 

 affording a very easy and exact method for reducing its indications to absolute measure. 

 I was much struck with the simplicity and excellence of Mr. Dellman's whole system 

 of observation on atmospheric electricity; and it has occurred to me that the Kew Com- 

 mittee might be disposed to adopt it, if determined to carry out electrical observations. 

 When I told Mr. Dellman that I intended to make a suggestion to this effect, he at once 

 offered to have an electrometer, if desired, made under his own care. I wish also to 

 suggest two other modes of observing atmospheric electricity which have occurred to 

 me, as possessing each of them some advantages over any of the systems hitherto fol- 

 lowed. In one of these I propose to have an uninsulated cylindrical iron funnel, about 

 7 inches diameter, fixed to a height of two or three yards above the highest part of 

 the building, and a light moveable continuation (like the telescope funnel of a 

 steamer) of a yard and a half or two yards more, which can be let down or pushed 

 up at pleasure. Insulated by supports at the top of the fixed part of the funnel, I 

 would have a metal stem carrying a ball like Dellman's, standing to such a height 

 that it can be covered by a hinged lid on the top of the moveable joint of the funnel, 

 when the latter is pushed up ; and a fine wire fixed to the lower end of the insulated 

 stem, and hanging down, in the axis of the funnel to the electrometer. When the 

 apparatus is not in use, the moveable joint would be kept at the highest, with its lid 

 down, and the ball uninsulated. To make an observation, the ball would be insu- 

 lated, the lid turned up rapidly, and the moveable joint carrying it let down, an 



1856. 2 



