81% Royal Society. 



odour. Oxide of tetraethylammonium, as the author calls this sub- 

 stance, saponifies the fats as readily as potassa. The experiment 

 was made with cocoa-nut oil, which, after half an hour's ebullition 

 ■with the new alkali, was converted into a beautiful soft soap, having 

 the appearance of an ordinary potassa soap. 



The author has traced the analogy of the new compound with 

 potassa in many other directions, and especially in its deportment 

 with the metallic oxides : his alkaloid, in fact, produces with the salts 

 of tiie metals exactly the same reactions as potassa. 



The other substances belonging to this group have similar pro- 

 perties, modified only by the character of the replacing molecules. 

 Among them are several whicii are remarkable for the complex 

 nature of their constitution, which, nevertheless, is perfectly intelli- 

 gible. 



In conclusion, the author draws attention to the assistance which 

 the solution of the grand problem of preparing artificially the natural 

 alkaloids, especially those of the cinchona bark, may i-eceive from a 

 further extension of these researches. He shows that even now the 

 analogy in the general deportment of his ammonium bases, and the 

 alkaloids of nature, is very great, although they difier materially in 

 many properties. 



A paper was read, entitled " Description and purpose of the glass 

 plate which bears the inscription ' Interferenz-spectrum. Longi- 

 tudo et celeritas undularum lucis relativa cum in acre turn in vitro.'" 

 By T. A. Nobert. Communicated by Michael Faraday, Esq., 

 F.R.S. &c. Received April 10, 1851. 



A rectangular plate of polished glass, 18 lines (Paris) in length, 

 9 lines in breadth, and V5 line in depth, has one of its longer narrow 

 faces ground so as to form an angle of 72° with its upper surface. 

 This narrow face is polished, the other three being ground at right 

 angles to the upper and under surfaces. On the upper surface, at 

 about the distance of 2 lines from the acute dihedral angle, twelve 

 systems of extremely fine parallel lines are cut, so that in each 

 system the lines are at perfectly equal distances, and the systems lie 

 separate from one another. Over these lines lies a thin covering 

 plate of glass, but at the place where the ruling is, a stratum of air 

 is contained between the plates. In these twelve systems, named 

 A, B, C, D, E, F, G, H, I, K, L and M, the respective distances of 

 the lines measured with great accuracy in Paris lines, are as follow : — 

 for A = 0-0003375 line. 



B = 0-0003063 



C = 0-0002625 



D = 0-0002438 



E = 0-0002250 



F = 0-0002063 



= 0-0001873 



H = 0-0001 750 

 1 = 0-0001625 



K = 0-0001500 



L = 0-0001375 



M = 0-0001281 



I 



