TRANSACTIONS OF SECTION A. 489 



The values obtained for " v " are (as far as I am aware) up to the present time 

 as follows : — 



MM. Weber and Kolraush 31-074 ohms. 



Sir W. Thomson 

 Professor 0. Maxwell . 

 Professors Ayrton and Perry 

 Velocity of light — M. Foucault 



28-2 

 28-8 

 29-80 

 29-8 



During the last twelve months we have been hard at work with the determination 

 of the electromotive force of contact of metals and liquids, using a new apparatus. 

 Some of the results are, we venture to think, most interesting ; for instance, the 

 electromotive force of contact of hot and cold mercury, no other conductors being in 

 contact with either mercury ; the electromotive force of contact of a cold metal and 

 hot mercury, no third conductor being in contact with either, &c, &c. The deter- 

 mination of the electromotive force of contact of the pairs of constituents of Mr. 

 Latimer Clark's constant mercurous sulphate cell was most laborious, and occu- 

 pied me weeks, in consequence of the difference of potential that exists between 

 the body of the mercurous sulphate paste and the layer of water that floats on the 

 surface. However, a forlorn hope kept me hard at it, and I am glad to say at last 

 I was successful in getting good results. We have gone over all the old ground 

 that furnished the basis of our former paper, as well as much new ground. 



Believe me to remain, dear Sir William, sincerely yours, 

 Professor Sir William Thomson, F.K.S., &c. W. E. Ayrton. 



It has been decided that the full account of the above determination of " v " 

 shall be given to the Society of Telegraph Engineers during the winter 1878-79. 



4. On Apparatus employed in Researches on Crookes's Force. 

 By Richard J. Moss, F.C.S. 



The author exhibited and described the apparatus which had been employed by 

 himself and Mr. (J. J. Stoney, F.R.S., in their researches on Crookes's Force. Early 

 in 1876 they devised a means of ascertaining the existence of a reaction between the 

 blackened vanes of a radiometer and the sides of the surrounding glass envelope. 

 A flat piece of elder-pith with one side blackened was attached by one end to the 

 inner surface of a small flask. A light glass arm suspended in the flask from a 

 silk fibre carried a disk of thin microscope glass which could be brought opposite 

 the blackened pith, and within a millimetre or two of it. When the flask was 

 exhausted it was observed that the pith when illuminated repelled the glass disk, 

 even when the tension of the residual air was equal to 7 m.m. of mercury. 

 Having obtained this result, another apparatus was constructed, with the view of 

 obtaining comparative measurements of the force at various tensions with a given 

 distance between the glass and the pith ; and at various distances with a given 

 tension of the residual gas. This apparatus is figured and described in the ' Proceed- 

 ings of the Royal Society,' 1877, p. 553. It was found that in an atmosphere of 

 hydrogen a Crookes's force was manifested at a distance of even 10 m.m., when the 

 tension of the residual gas was as much as 5 m.m. of mercury. Within certain 

 limits the force was found to vary about inversely as the tension ; and at a given 

 tension the variations produced by alterations in the distance between the pith and 

 the glass were nearly inversely as the distance until it exceeded 20 m.m. (half the 

 diameter of the containing tube), when the force remained almost constant, even at 

 a distance of 100 m.m., the maximum of which the apparatus admitted. 



5. On Spheroidal Drops. By Richard J. Moss, F.C.S. 



According to Mr. G. J. Stoney's recently published theory of the spheroidal state, 

 the drops are supported by the pressure which is exerted between hot and cold 

 surfaces when they are within a certain distance from one another, depending on the 



