38 



Anniversary Meeting, 



[Nov. 30, 



to conduct till a little of the alkali is vaporized by heating them, and the 

 gradual progress of the exhaustion gives a wide range of observation. 



5. The current of an induction machine is necessarily intermittent, and 

 it has been supposed that the strata are in some way caused by the inter- 

 mittence, and are possibly connected with the mode of action of the contact- 

 breaker. Mr. Gassiot has, however, shown that they are perfectly developed 

 in the discharge of an extended voltaic battery through exhausted tubes. 

 The large water-battery already mentioned shows them in great beauty ; 

 the discharge, however, is still intermittent. 



6. The same appearance is exhibited by a Grove's battery of 400 well- 

 insulated cells ; but in this case a new and remarkable phenomenon pre- 

 sents itself. At first the discharge resembles that obtained from the water- 

 battery, and is like it intermittent ; but suddenly it changes its character 

 from intermittent to continuous (so far at least as can be decided by a revolv- 

 ing mirror), and everything indicates that we have now the true voltaic arc. 

 The discharge is now of dazzling brilliancy, and is stratified as before, whence 

 it appears that strata are capable of being produced by the true arc discharge. 



7. This change is accompanied by a remarkable alteration in the heating 

 of the two electrodes. Mr. Gassiot had previously shown that, in the ordi- 

 nary voltaic arc, formed in air of the usual pressure, the positive electrode 

 is that which is the more heated, whilst in the discharge of an induction 

 machine, whether sent through air at the ordinary pressure between elec- 

 trodes of thin wire, or through an exhausted tube, it is the negative. The 

 discharge through the large Grove's battery, so long as it was intermittent, 

 agreed with the induction discharge in this character as in others, that the 

 negative electrode was that which became heated ; but when the discharge 

 suddenly and spontaneously passed from the intermittent to continuous, 

 the previously heated negative electrode became cool, and the positive was 

 intensely heated. 



These brief references will suffice to show what a high place Mr. 

 Gassiot holds amongst those who are investigating this new track, which 

 promises such great advance in our knowledge of those molecular forces 

 in the study of which all physical science must ultimately centre. I may 

 be permitted to add, that in his whole career he has sought not his own 

 fame, but the advancement of science ; he has rejoiced as much in the dis- 

 coveries of others as in his own, and aided them by every appliance in his 

 power. I cannot refrain from mentioning a recent instance in which this 

 liberal and unselfish spirit has been strikingly exhibited. He has had exe- 

 cuted a grand spectroscope, furnished with no less than nine faultless prisms, 

 a design in which he has been ably seconded by the skill of the optician 

 Mr. Browning, to whom the construction was entrusted. This magnificent 

 instrument he has placed at the disposal of any Fellow of the Society who 

 may happen to be engaged in researches requiring the use of such powerful 

 apparatus. The instrument is at present at the Kew Observatory, where 

 it is in contemplation to undertake the construction of a highly elaborate 

 map of the spectrum. 



