207 



vessel. The communication with the sea is made by tubes brought 

 from the bottom at midships to the cabin, where the glass tubes 

 and scale are placed ; and the rate of sailing may at all times be 

 known by observing the length of the column of oil displaced. 



3. A verbal communication on the Osseous Structure of 

 Fishes. By Dr Macdonald. 



Monday \Gth April. 



Sir T. M. BRISBANE, Bart. President, in the Chair. 

 The following donations were presented : — 



Comptes Rendus Hobdomadaires des Seances de I'Acaderaie des 

 Sciences. 1838. 1" Semestre. No. 13 By the Academy. 



A Systematic and Stratigraphical Catalogue of the Fossil Fish in 

 the Cabinets of Lord Cole and Sir Philip Grey Egerton. By 

 Sir Philip Grey Elgerton, Bart. — By the Author. 



The following communications were read : — 



1. Researches on Heat. Third Series. By Professor Forbes. 



This paper is divided into tluree sections, each containing a dis- 

 tinct investigation. 



The First Section is on the Variable Polarizability of different 

 kinds of Heat. This fact, namely, that when polarization takes 

 place by refraction through a bundle of pai-allel mica plates, some 

 kinds of heat are less completely polarized than others at the same 

 incidence, the author proposed to establish in the second series of 

 hi« researches. His investigations, however, having been con- 

 sidered by some persons as open to objection, and directly contrary 

 results having been obtained by M. Melloni in his repetition of these 

 experiments, the author was induced to investigate the subject anew 

 and with every precaution. He used rays of heat rendered pa- 

 rallel by a rock-salt lens, previous to falling on the mica plates, 

 which were removed to a distance from the pile ; but still the dif- 

 ferences in the Parallel and Crossed positions of the mica bundles 

 when heat of various qualities was used, were as unequal as for- 

 merly ; and having varied the experiment in different ways, the 

 author concludes by adhering to his former conclusion, and gives 

 the following table of the proportions of the heat penetrating the 

 mica plates when parallel, which were stopped in their crossed po- 

 sition : — 



