22 : REPORT—1862. 
ture in Centigrade degrees, measured from the temperature of melting ice. 
Prof. W. Thomson has been led, from calculations based upon Regnault’s observa- 
tions on the pressure and latent heat of steam, to the conclusion that p cannot in 
all cases be expressed by the above formula. 
May not the deviations, however, be entirely due to the influence of cohesion ? 
It is evident that cohesion must affect the value of this function in the following 
manner: if a mutual attraction exist between the particles of a gas at a given 
temperature, then that gas in cooling itself down one degree below that tempera- 
ture, by performing mechanical work in expanding, will execute less work than it 
would otherwise do did no cohesion between the particles exist; for a portion of the 
heat must be consumed in work against the cohesion. The quantity consumed by 
cohesion will continually increase as the temperature diminishes; for as the tem- 
perature diminishes the cohesion increases. But in regard to steam and all other 
saturated vapours, the reverse holds true, for the cohesion of the particles of vapours 
increases as their temperature rises, because their density increases with rise of tem- 
perature. In the case of a perfect gas, the function will agree with the formula at 
all temperatures ; but in imperfect gases and vapours the function will deviate from 
the formula, but in opposite directions. In both cases the actual function will fall 
short of the ges 
On the Supernumerary Bows in the Rainbow. By the Rev. J. Duxexz. 
The author gave a method of approximating to the size of the drops of rain 
corresponding to any given position of the supernumerary bows produced by the in- 
terference of the two luminiferous surfaces proceeding from each drop. It appeared 
from his tables appended to the paper that the size which Dr. Young (without 
giving his method of calculation) had assigned to the drops under certain conditions 
was within 5;/;;th of an inch of the truth, and was more accurate than that assigned 
subsequently by Mr. Potter. 
On the Duration of Fluorescence. By Dr, Essripacu. 
The author described the apparatus by which he succeeded in 1856 in proving 
the duration of fluorescence (z;1;5 second with uranium glass), thereby establishing 
a year before M. Becquerel the experimental link between this interesting pheno- 
menon and phosphorescence. 
Description of an Optical Instrument which indicates the Relative Change of 
Position of Two Objects (such as Ships at Sea during Night) which are 
maintaining Independent Courses. By J. M. Menzies. 
This instrument consisted of a lantern-shaped case, containing a lens in front 
and a coacentric sheet of bent glass behind, at the focal distance of the lens, ruled 
with parallel vertical lines. This was hung up on gimbals so as to have its axis 
parallel to the course of the vessel, and the biight spot (the image of the light of the 
approaching vessel) showed by its position ‘cal shifting the relative place and course 
of the approaching vessel. 
Experiments on Photography with Colour. By the Rev. J. B. Reapr, F.2.S. 
A recent examination of the phenomena of polarized light in their immediate 
connexion with the undulatory theory led the author to inquire into the causes of 
natural colours, and thence to the possibility of coloured objects setting up, in sen- 
sitive films on which their image is thrown, the very same causes which regulate and 
determine their own respective colours. This being effected, the image of an object 
would communicate to the eye the identical colour of the object itself. 
The propositions, in general terms, are—that radiant-coloured light consists in un- 
dulations of the luminiferous ether—that all material bodies have an attraction for 
the ethereal medium, by means of which it is accumulated within their substance 
unit, divided by the absolute temperature. The reciprocal of E must be the absolute tem- 
perature of melting ice, or the formula is erroneous: 
