440 Prof. A. Dendy. 



results : A globe of 32'35 c.c. capacity, 1 filled at a pressure of 

 765'G mm., and at the temperature 17'43, weighed 0'05442 gram. 

 The density is therefore 19'87. A second determination, made after 

 sparking, gave 110 different result. This density does not sensibly 

 differ from that of argon. 



Thinking that the gas might possibly prove to be diatomic, we 

 proceeded to determine the ratio of specific heats : 



Wave-length of sound in air 34 '18 



gas 31-68 



Ratio for air 1-408 



gas. 1-660 



The gas is therefore monatomic. 



Inasmuch as this gas differs very markedly from argon in its 

 spectrum, and in its behaviour at low temperatures, it must be 

 regarded as a distinct elementary substance, and we therefore pro- 

 pose for it the name " metargon." It would appear to hold the 

 position towards argon that nickel does to cobalt, having approxi- 

 mately the same atomic weight, yet different properties. 



It must have been observed that krypton does not appear during 

 the investigation of the higher-boiling fraction of argon. This is 

 probably due to two causes. In the first place, in order to prepare it, 

 the manipulation of a volume of air of no less than 60,000 times the 

 volume of the impure sample which we obtained was required ; and in 

 the second place, while metargon is a solid at the temperature of boiling 

 air, krypton is probably a liquid, and more volatile at that temperature. 

 It may also be noted that the air from which krypton has been 

 obtained had been filtered, and so freed from metargon. A full 

 account of the spectra of those gases will be published in due course 

 by Mr. E. C. C. Baly. 



" Summary of the principal Results obtained in a Study of the 

 Development of the Tuatara (Sphenodon punctatum)" By 

 ARTHUR DENDY, D.Sc., Professor of Biology in the Canter- 

 bury College, University of New Zealand. Communicated 

 by Professor G. B. HOWES, F.R.S. Received June !, 

 Read June 16, 1898. 



Thanks to the most generous and freely rendered services of Mr. 

 P. Henaghan, Principal Keeper of the Lighthouse on Stephen's 

 Island in Cook Straits, I have lately obtained a very perfect series of 

 Tuatara embryos, ranging in age from just before the appearance of 

 the blastopore to about the time of hatching. I have classified these 

 embryos in sixteen stages, and propose shortly to publish a general 



