12 REPORT — 1859. 



On the Relation between Refractive Index and Volume among Liquids. 

 By the Rev. T. P. Dale and J. H. Gladstone, Ph.D., F.R.S. 



The authors referred to a previous paper, in which they had shown, among other 

 things, that the sensitiveness of a substance is not directly proportional to the change 

 of density produced by an alteration of temperature. The theoretical formulae re- 

 lating to the dispersion of light afford little assistance in determining what this rela- 

 tion is, but a series of careful observations had been made with a view of arriving at 

 some empirical formula. It was found that the product of the volume, reckoned as 

 1000 at the boiling-point, and the refractive index for the line A of the prismatic 

 spectrum less unit}', gave numbers which were nearly constant. In the case of 

 water, alcohol, pure wood-spirit, and bisulphide of carbon, however, the volume 

 increases a little faster in proportion than the refractive index less unity diminishes, 

 while with ether the reverse is the case. The regularity of the numbers shows that 

 this is not due to errors of experim nt. The authors propose examining the subject 

 more closely. 



On the Theory of Light. By G. F. Harrington. 



Notice of Experiments on the Heat developed by Friction in Air. 

 By J. P. Joule, LL.D., F.R.S. 



The research which Professor Thomson and myself have undertaken on the ther- 

 mal effects of fluids in motion, naturally led us to examine the thermal phenomena 

 experienced by a body in rapid motion through the air. The experiments which we 

 first made for this purpose were of a very simple kind. We attached a string to the 

 stem of a sensible thermometer, and whirled it alternately slowly and rapidly. In 

 this way we uniformly obtained a slight effect ; there was a higher temperature 

 observed immediately after rapid, than after slow whirling. A thermo-electric junction 

 rapidly whirled also gave us an appreciable thermal effect, indicated by the deflection 

 of the needle of a galvanometer. 



Afterwards a more accurate set of experiments was made by us ; using a lathe, 

 to the spindle of which an arm was attached carrying one of Professor Thomson's 

 delicate ether or chloroform thermometers. The thermometers employed were so 

 extremely sensitive that each division of their scales had a value of not more than 

 ■j^o of a degree Centigrade. The great value of Professor Thomson's thermo- 

 meters in the whirling experiments,' was further enhanced by the light specific gravity 

 of ether comparatively with mercury : the pressure produced by centrifugal force ope- 

 rating on a long column of mercury, would have probably broken a mercurial 

 thermometer whirled at high velocity. 



The results arrived at by Professor Thomson and myself were as follow : — 



1st. The rise of temperature in the whirled thermometer was, except at very slow 

 velocities, proportional to the square of the velocity. 



2nd. The velocity at which the bulb had to travel in order that its temperature 

 should be raised 1° Cent, was 182 feet per second. 



3id. At very slow velocities the quantity of thermal effect appeared to be some- 

 what greater than that due from the square of the velocity calculated from the above 

 datum ; and we surmised that this was owing to a sort of fluid friction different 

 from the source of resistance at high velocities. We therefore made several attempts 

 to increase this fluid friction ; the most successful result being obtained by wrapping 

 fine wire over the bulbs. By this means we succeeded in obtaining the V° from a 

 velocity of 30 feet per second, a quantity five or six times as great as that which took 

 place when the naked bulb was revolved at the same velocity. 



We resumed the whirling experiments last May ; and it is owing to the circum- 

 stance that it has happened that I have myself been principally engaged in making 

 those which I am about to communicate to the Section, that Professor Thomson has 

 requested me to give an account of this part of our joint labours. 



Our object was to repeat the former experiments under new circumstances, so as 

 to verify and extend the results already obtained. A very brief outline can only be 

 given in this place, as we intend shortly to incorporate them in a joint paper for the 

 Royal Society, to whose assistance we owe the means of prosecuting the inquiry. 



