40O Royal Society. 



gree of heat. He described a combination of this acid 

 wilh water, likewise a crystalline solid, very combustible, 

 and when decomposed by heat affording a peculiar elastic 

 fluid absorbable by water, not si5i)ntanei;usly inflammable, 

 antl consisting of phosphorus united to two volumes of hy- 

 drogen condensed into the space of one volume, and which 

 he propcjses lo call lujdrophosphorlc gas. 



He entercil into the detail of sonie experiments on sul- 

 phuric acid, which, he staled, cannot exist independently of 

 the presence of water; and he described a solid compound 

 o\ nitrous acid gas, sulphurous acid cfas, and water. He 

 considered all the facts advanced in this paper as aflfording 

 confirmations of the theory of definite proportions. And 

 he drew some general conclusions respecting the impor- 

 tance of water as a chemical agent. Most of the bodies 

 called ox/t?i?.v, when precipitated from aqueous solutions, are 

 jn truth (said Sir H. Davy) hydrals ; and their colours and 

 their properties depcu'l upon the combined water. 



Jiatc II. — Dr. VVoilaston ""read to the Society a short 

 paper on improvements in the camera obscura and simple 

 microscope, founded on the same periscopic principles by 

 which he improved the construction of spectacles a few 

 years since*. 



In his camera obscura the light is admitted through a 

 circular opening to the concave surface of a large meniscus 

 placed behind it, at such a distance that all pencils of ravs 

 pass nearly at right angles through its posterior surface. 

 Hence those that come from objects obliquely situated, 

 form more distinct images, and afford a larger field of view 

 than is obtained by the common construction. 



His microscope consists of two plano-convex lenses with 

 their flat surfaces tov\ ards each other, but prevented from 

 touching by a thin pl-ate of metal. A small perforation in 

 the centre of the metal hufl^'rs no rays to pass but what are 

 at right angles to both the exterior surfaces, and hence give 

 a distinct field of view of ertiat extent. 



He observes also that the camera lucida in Its most sim- 

 ple form, with the upper surface of its prism concave, has 

 the same advantage as the periscopic construction. 



GEOLOGICAL SOCfETV. 



May 1, 1812. The president in the chair. — A paper by 

 Dr. M'Culloch (member of the Soclel\), " On Bistre and 



• Philosophical Magazine, vol. iviii. p. 1G5. 



Other 



