of Edinburgh, Session 1881-82. 
361 
“ Some of the properties of the medium 
g = J a 2 + y 2 
(hut not the double-image property) are deduced in my second paper 
on ‘Mirage’ (Phil. Mag., April 1873), sect. xvii. (6). See also 
Bradford B. A. Report , p. 37, for a triple imago effect obtained 
experimentally with an arrangement of two liquids — brine below, 
water above.” 
Note added by Professor Everett, December 31, 1881. 
Having had an opportunity of reading the foregoing abstract, I 
desire to express my appreciation of the precision with which Pro- 
fessor Tait’s method determines how many images, and whether 
erect or inverted, will be visible from a given point. Its practical 
application, however, appears to be somewhat laborious. 
The investigation given in the abstract really confirms my result, 
that with the assumption 
g = Ja 2 + y 2 
not more than two images can be seen from a given point in the 
air ; for the value of g at a point from which three are seen must 
exceed J5, whereas in reality g in the atmosphere never exceeds 
1-0005. 
BUSINESS. 
The following candidates were balloted for, and declared duly 
elected Fellows of the Society : — —Sir Peter Coats, and Mr Andrew 
Young. 
Monday , 19 th December 1881. 
DAVID MILNE HOME, LL.D., Vice-President, 
in the Chair. 
MAKDOUGALL-BRISBANE PRIZE. 
The Council having awarded the Makdougall-Brisbane 
Prize, for the biennial period 1879-80, to Professor Piazzi 
Smyth, Astronomer-Eoyal for Scotland, for his Memoir, 
entitled “The Solar Spectrum in 1877-78, with some practical 
