TEANSACTIONS OF SECTION A. 251 



•were washed in hot water, wiped and polished, and passed over the spirit-lamp 

 while still hot. After observing a difference in the first two specimens examined, 1 

 made preliminary experiments on the other two before cleaning them. The follow- 

 ing are the results obtained : 



Hard Crown Glass. 



S.I.C. 



Christmas 1877 3108 



August 7, 1879. — Not wiped for more than a year ; placed in balance covered 



with dust exactly as taken from box, which does not shut airtight . . 3-236 

 •August 8.— Cleaned in hot water, as described above 3-310 



Light Flint Class. 



S.I.C. 



Christmas 1877 3-01 



August 4, 1879. — Dusted lightly with duster, not rubbed 2-90 



August 4. — Cleaned in hot water, experimented on while hot .... 3-44 



August 4. — Cooled under tap, wiped with glass cloth 3-44 



August 5. — Had stood twenty-four hours uncovered on table, not wiped . . 3-39 



August 5. — Smeared all over with oil 3-48 



August 5. — Smoked on oily surface over paraffin lamp, so as to make glass 



semi-opaque 3-46 



August 5. — Glass made very wet with solution of sal-ammoniac . Experiment 



impossible 

 August 5. — Eoughly dried with duster ; surface appeared opaque, like ground 



glass .............. 1-64 



August 5. — Wiped over with glass-cloth, but not rubbed 2-36 



August 5. — Einsed under cold tap, and wiped with glass-cloth, but not polished 3-46 

 August 5. — While still cold, passed over spirit-lamp till much more clouded 



than ever would be the case in actual work ; placed in balance, and 



experiment made as quickly as possible . . . . . . 3-48 



My conclusion from the above numbers is, that although it is possible by 

 sufficiently wetting the surface of the plate to produce any apparent reduction of 

 the specific inductive capacity, yet that even if very much less care had been taken 

 to clean the plates than was taken in 1877, the greatest quantity of moisture that 

 could accidentally have been left on them would have been totally incapable of 

 producing anything bike the difference now under examination. 



I am therefore led to the conclusion that in the course of a year and a half an 

 actual change has taken place in the glasses, which is shown by a considerable real 

 increase in their specific inductive capacities. To complete our knowledge of this 

 new phenomenon we require a series of monthly observations, extended over 

 perhaps a period of several years. I shall hope to be able to give the results of 

 another year's experiments at the next meeting of the Association. 



These experiments have some importance as regards Professor Clerk Maxwell's 

 electro-magnetic theory of light. In a recent lecture 1 I ventured to suggest ' that 

 it is quite possible that the relation between electric induction and light exists — 

 namely, that they are disturbances of the same ether, but that there is some un- 

 known disturbing cause affecting the electric induction.' 



Possibly a clue to the nature of this disturbing cause may be found in the fact, 

 that the specific inductive capacities are affected by some of the changes which 

 chemists tell us are constantly going on in glasses, but that these changes do not 

 affect the refractive indices. 



6. On the Cause of Bright Lines in the Spectra of Comets. 

 By G. Johnstone Stoney, M.A., F.B.S., H.B.I.A. 



Dr. Huggins and other observers have seen the bright lines of some compound 

 of carbon in the spectra of several comets. This establishes the fact that a com- 

 pound of carbon is present in the comets. It is always assumed in what has been 



1 Royal Institution, February 6, 1879. 



