438 Prof. TyndalPs Contributions to Molecular Physics, 



in question sufficiently great to prevent the manifestation of 

 molecular attraction. 



An interest is given to these experiments by the fact that 

 capillary actions make themselves felt therein at far greater dis- 

 tances (20 millims. to 25 millims.) than with the bodies usually 

 employed in order to exhibit these actions in physical lectures. 

 I may add that, in spite of the smallness of the masses which 

 act upon one another, all these movements may be followed with 

 the greatest facility, in consequence of the large quantity of 

 light reflected by the non-submerged zones. 



The effect of the cohesion between two spherules in juxta- 

 position enabled me to increase gradually the volume of the 

 initial globule. For this purpose, it was merely necessary to 

 float successively several very small spherules, which ultimately 

 all united themselves to the first globule. I was thus enabled 

 to seek experimentally the maximum diameter of a sphere able to 

 maintain itself at the surface of distilled water. I found it to be 

 very nearly 087 of a millimetre. With well-water, I found 

 the maximum diameter to be about 1 millimetre. 



I also tried to make droplets of mercury float on olive oil, 

 and succeeded perfectly ; the globules, however, had at most a 

 diameter of a third of a millimetre. 



These experiments suggested the idea of floating small solid 

 spheres of great density. To cite one case only, a spherule of 

 platinum 0*3 to 0*4 of a millimetre in diameter, was easily made 

 to float on the surface of water. 



In the last place I submitted several saline solutions to expe- 

 riment ; amongst others, solutions of chloride of sodium, nitrate 

 of barytes, and carbonate of soda. It appeared to me that the 

 maximum diameter increased at first with the degree of concen- 

 tration, but that this augmentation had a limit, beyond which 

 the maximum diameter diminished. I propose, however, to 

 examine this point more closely on some future occasion. 



LIV. The Bakerian Lecture. — Contributions to Molecular Physics. 

 Being the Fifth Memoir of Researches on Radiant Heat. By 

 John Tyndall, F.R.S., #c* 



§ I. Preliminary considerations. — Description of apparatus. 



THE natural philosophy of the future must, I imagine, 

 mainly consist in the investigation of the relations 

 which subsist between the ordinary matter of the universe and 



* From the Philosophical Transactions, Part II. 1864, having been read 

 at the Royal Society March 17, 1864. 



