602 



made in similarly constructed tubes by M. Pliicker (Phil. Mag. 

 August 1858), but finding it impracticable to ascertain with accu- 

 racy the nature of the residual gas, he reluctantly laid them aside. 

 All the vacuum-tubes in which his experiments were made, were 

 prepared by himself or in his presence ; as each was exhausted and 

 hermetically sealed, it was marked with a consecutive number ; up- 

 wards of 100 were thus prepared; many were broken or otherwise 

 destroyed, but the remainder he retains with the original numbers 

 for future reference. The author uses several terms, which he ex- 

 plains : air, hydrogen, oxygen, or nitrogen (mercurial) denote that 

 the vacuum-tube contains vapour of mercury plus the air or gas 

 remaining in the tube with which it was filled previous to the in- 

 troduction of the mercury : he applies the terms outer positive or 

 negative, and inner positive or negative, to denote the character of 

 the discharge from the terminals ; conductive and reciprocating de- 

 note the peculiar conditions of discharges from an induction appa- 

 ratus when taken in vacuum-tubes ; with a conductive discharge the 

 needle of a galvanometer placed in the circuit will be deflected, as 

 are also the stratifications on the approach of a magnet they having, 

 as the author has shown in his former communication, a tendency to 

 rotate as a whole round either pole, but in contrary directions ; in a 

 reciprocating discharge the stratifications are confused, they are 

 divided or separated by the magnet, and the needle of a galvanometer 

 placed in the circuit is not deflected. 



The author explains the condition which the stratified discharge 

 assumes if any air or gas remains or is subsequently introduced into 

 a Torricellian vacuum, and describes what he denominates a white 

 and a blue tongue discharge, which under certain conditions always 

 appears at the negative terminal. In Torricellian vacua, if air or 

 nitrogen is introduced, the stratifications, exclusive of their altered 

 form, exhibit a red colour, while when hydrogen or oxygen is added, 

 they retain the bluish-grey appearance : when the ends of the tubes 

 were punctured by means of an electrical spark from a machine, the 

 air or gas could be admitted so gradually as to occupy two or three 

 hours in the experiment, and in this manner the preceding results 

 were obtained. 



In the best Torricellian vacua the author has been able to obtain, 

 the stratifications always assumed a long cloud-like appearance ; by 



