56 Royal Society. 



the whole work is open to the same remark. Still, it is highly probable 

 that the heat of vapour plays a more important part in meteorological 

 phenomena than has hitherto been generally supposed, and Mr. 

 Hopkins has done a real service to the science by calling attention 

 to this point. If he has attributed rather too much to this particular 

 cause, it is only what is generally done, and might naturally be ex- 

 pected, whenever a person discovers the importance of some cause 

 hitherto neglected. 



In treating of other points, such as the fluctuations of the baro- 

 meter, dew, &c, our author does not appear to have availed himself 

 sufficiently of the recent researches of Dove, Melloni, and others. 

 The subject of ' dew' in particular has received the greatest accession 

 of illustration and explanation by the labours of Melloni, to which 

 Mr. Hopkins makes no reference whatever. We also meet with 

 some expressions in the course of the work which indicate rather 

 loose notions of elementary scientific principles ; as, for instance, at 

 page 72, where the author speaks of a current being "forced up " the 

 sides of elevated land " by its inertia." 



Upon the whole, however, the work is written in a scientific spirit, 

 and indicates considerable care and labour in the collection of facts. 

 Moreover, it is eminently suggestive, and therefore likely to be of 

 still greater service by leading to further inquiries. 



XI. Proceedings of Learned Societies. 



ROYAL SOCIETY. 



[Continued from vol. viii. p. 553.] 



June 15, 1854. — The Earl of Rosse, President, in the Chair. 



THE following papers were read : — 

 " On the Structure of certain Microscopic Test-objects, and their 

 Action on the Transmitted Rays of Light." By Charles Brooke, 

 M.A., F.R.S. 



In order to arrive at any satisfactory conclusions regarding the 

 action of any transparent medium on light, it is necessary to form 

 some definite conceptions regarding the external form and in- 

 ternal structure of the medium. This observation appears to apply 

 in full force to microscopic test-objects ; and for the purposes of the 

 present inquiry it will suffice to limit our observations to the struc- 

 ture of two well-known test-objects, the scales of Podura plumbea, 

 and the siliceous loricre or valves of the genus Pleurosi,g?na, freed 

 from organic matter : the former of these is commonly adopted as 

 the test of the defining power of an achromatic object-glass, and the 

 several species of the latter as the tests of the penetrating or sepa- 

 rating power as it has been termed. The defining power depends 

 only on the due correction of chromatic and spherical aberrations, so 

 that the image of any point of an object formed on the retina may 

 not overlap and confuse the images of adjacent points ; this correc- 

 tion is never theoretically perfect, since there will always be residual 

 terms in the general expression for the aberration, whatever prac- 



