PROCEEDINGS OF SOCIETIES. 
53 
the surface tension consequent upon the alteration of temperature, it 
followed that light particles below the surface of water should be 
attracted by heat and be subject to vibratory motion. Mr. Hartley 
then proceeded to read a paper in continuation of his former ob- 
servations (see p. 8). 
Mr. Slack asked if Mr. Hartley intended to use the word attrac- 
tion to characterize the movement he had described, or would he not 
state it as a motion in the direction of least resistance. 
Mr. Hartley said he should, of course, have said apparent attraction, 
because, though it appeared as if the bubble was attracted, it was really 
shot forward from behind, as from a catapult. When plumbago was 
floating upon the surface of the water it was repelled by a hot wire, 
the alteration in surface tension causing the liquid to shrink away 
and carry the wetted particles along with it ; but when it had been 
left on the surface for some hours the shrinking away was less. 
Mr. Slack inquired if Mr. Hartley had tried electricity ? The 
old observers said that only heat affected the Brownian motion. 
Mr. Hartley said he had tried electricity, but found that, with 
the current from six cells of Grove’s, a heating effect was produced 
which rendered the result uncertain ; he had also tried experiments 
by passing sparks, but could not do this very well because of the large 
amount of metal about the microscope. He could not say what might 
be the effect of a magnet. 
The thanks of the meeting were then unanimously voted to 
Mr. Hartley for his paper. 
The Chairman then intimated that the meeting would be adjourned 
to the first Wednesday in October. Notice was also given that in 
accordance with their usual custom the Society’s rooms would be closed 
during the month of August. At the close of the meeting, Mr. Hartley 
exhibited an interesting experiment with white arsenic powder. 
Throwing a little upon water, it was found that some particles were in 
a film of air and floated in the liquid. On bringing a small mass of 
heated metal near these globules, they moved towards it. The expla- 
nation being, that the water acted upon by the heat opposed less 
resistance than the cooler water behind, and the bubble was thus pro- 
pelled forward as if attracted by the metal. 
Donations to the Library and Cabinet since May 2 : 
From 
Nature. Weekly The Editor. 
Athenaeum. Weekly Ditto. 
Society of Arts Journal Society. 
Bulletin de la Societe Botanique de France Ditto. 
American Journal of Microscopy. 3 parts Editor. 
Papers and Proceedings of the Royal Society of Tasmania, 
1875 Society. 
Considerations on Vegetable Nutrition. By Salvador Calderon. 
1877 Author. 
Five Photographs of Physalia pelagica Dr. ffabirshaw , of 
' New York. 
Six Slides of Double-stained Vegetables W. H.Walmsley 
of Philadelphia. 
The following gentlemen were elected Fellows of the Society : — 
