Intelligence and Miscellaneous Articles. 41 L 



The number 5622 Mr. Capron ■ has taken by mistake from the 

 wrong series of numbers — from spectrum No. I. instead of from 

 spectrum No. II. The other two numbers, 5189 and 4829, I am 

 not able to find in the ' Index of Spectra ' at all. The wave-lengths 

 actually given for the three lines of the ^6e-spectrum are as fol- 

 lows : — 



Spectrum No. II. 



j 58 5602 



'& 74 5195 



I 92 4834 



I have satisfied myself that these lines are due to a compound of 

 carbon and oxygen ; and their production in tubes supposed to con- 

 tain oxygen is not at all surprising. The results obtained by the use 

 of vacuum-tubes must always be received with caution, since it is 

 almost impossible to form any certain conclusion as to the real 

 nature of the small quantity of gas remaining in the tube, even 

 when one has filled the tube one's self ; and in the case of tubes pur- 

 chased from makers of such apparatus, the nature of the contents 

 is simply a matter of conjecture. 



I am, <fcc, 



W. Maeshall Watts. 

 Giggleswick Grammar School, 

 April 14, 1875. 



EXPERIMENTS WITH THE HOLTZ MACHINE. BY P. ROSSETTI*. 



In a recent series of experiments upon the Holfcz machine, first 

 pattern, M. Rossetti sought to determine in what measure the in- 

 tensity of the current produced depends on the velocity of rotation 

 of the machine, on the work expended, and on the humidity of the 

 air, to estimate its electromotive force, internal resistance, &c. The 

 results at which he arrived on these points are the following. 



In one and the same series of experiments, the intensity of the 

 current is very sensibly, but not exactly, proportional to the velocity 

 of rotation of the plate ; the intensity increases a little more rapidly 

 than the velocity of rotation. 



The effect is modified by the humidity of the air, the velocity 

 necessary to produce a certain intensity being greater in wet than 

 in dry weather. 



The work expended for the production of the electricity is exactly 

 proportional to the intensity of the current. It was measured by 

 the difference of the weights necessary to impress a certain 

 velocity on the plate, according to whether the machine was charged 

 or not. 



* Nuovo Cimento, Ser. 2, vol. xii. p. 89. 



