June 24 J909J 



NATURE 



507 



ture in expansion is rather less than in compression, and 

 therefore the loss is not divided equally between the two. 



The results of experiments made in this way give values 

 of the specific heat at constant volume which increase 

 more than 30 per cent, in the range from 100" C. to 

 1500° C, and tend to a limit at high temperatures, while 

 the observations indicate that this apparent change is 

 accompanied by continued combustion. 



Experiments made since the report was issued show 

 that, relative to the mean temperature, the heat loss for 

 air during compression is greater than the loss during 

 expansion ; these experiments will be continued to ascer- 

 tain if such is the case for a gas-engine mixture. 



In concluding its discussion of explosion experiments 

 the committee expresses the opinion that " values of the 

 energy obtained from explosion records are not subject to 

 any very great errors on account of heat loss by conduc- 

 tion to the walls of the vessel, or on account of incom- 

 plete combustion, but that they are affected by errors of 

 quite unknown amount due, first, to heat radiated, and, 

 secondly, to the want of thermal equilibrium at the time 

 when the pressure is measured. For the purpose of test- 

 ing the first of these conclusions it is very desirable that 

 further experiments should be made on explosions in 

 vessels of greatly different size, but of similar form. The 

 opinion entertained by the committee that incomplete com- 

 bustion is a surface-phenomenon, on which this conclusion 



as to the validity of the method is based, also requires 

 further confirmation. As regards the second conclusion, 

 further experiment on the actual amount of heat radiated 

 by burning gas is urgently required, and also experiments 

 to confirm or negative the effect of the nature of the wall 

 surface upon the pressure reached in an explosion. The 

 effect of want of thermal equilibrium can be determined 

 up to a point by calculation ; but before such calculation 

 can be usefully made, it is desirable that further informa- 

 tion should be obtained as to the temperature distribution 

 after an explosion, especially in the neighbourhood of the 

 walls." 



In view of the importance of measurements of tempera- 

 ture in connection with gas explosions, the committee 

 considers it desirable that the relations between pressure, 

 volume, and temperature of gas thermometers should be 

 determined at very high temperatures. The nitrogen 

 thermometer has been used with an iridium bulb up to 

 1600° C, but no other gas has been tested beyond 1100° C. 

 The chief difiiculties in carrying out comparisons of gas 

 thermometers have been the absence of any material which 

 is impervious to the gas and sufficiently refractory to 

 withstand very high temperatures. Dr. Harker believes 

 that he is now in possession of a material suitable for 

 gas thermometry up to 1800° C, and he has suggested 

 that an attempt be made to compare thermometers using 

 nitrogen and argon at the highest temperatures possible. 

 If they agree, the probability is in favour of both being 

 in substantial agreement with the thermodynamic scale, 

 but if it is found that they differ, the presumption will be 

 that the argon thermometer is in closer agreement with 



XO. 2069, VOL. 80I 



the thermodynamic scale, as this gas is- supposed to be 

 monatomic and incapable of dissociation. The committee 

 hopes that it will be possible to carry on a research of this 

 kind, and that the resources of the National Physical 

 Laboratory will be available for the inquiry. 



The report concludes with a note by Prof. Callendar, 

 printed in full as an appendix, and containing a critical 

 examination of the experimental work on " the deviations 

 of actual gases from the ideal, state, and on experimental 

 errors in the determinations of their specific heats." 



E. G. COKER. 



" CHEMICAL" EMBRYOS. 

 COME very remarkable observations have been made 

 from time to time during the last twenty years on 

 the effect of chemical stimuli in bringing about abnor- 

 malities in developing embryos. The " Lithium larvse " 

 of the sea-urchin and of the frog, obtained by Herbst and 

 Morgan, are familiar examples of this class of phenomena, 

 but perhaps the most remarkable is the " Magnesium 

 embryo " of the fish, FunduUis heteroclitus, described by 

 Charles R. Stockard in the February number of the 

 Journal of Experimental Zoology. A large percentage of 

 the embryos of this fish, when subjected during their 

 development to the influence of magnesium salts dissolved 

 in sea-water, are found to possess a single median or 

 " Cyclopean " eye in place of the ordinary pair. These 

 embryos may hatch and swim about in a perfectly normal 

 manner, and the single eye is evidently fully functional. 

 The mouth is displaced ventrally, and gives rise to a 

 proboscis-like structure, but, unfortunately, no attempt 

 was made to feed the embryos, so that we do not know 

 how long they might live after the absorption of the food- 

 yolk. The abnormality was present in varying degrees in 

 different cases, ranging from embryos in which the eyes 

 were merely unusually close together, through what we 

 may perhaps call the typical cyclopean condition, to others 

 in which no eye at all was developed. 



A second type of monster, with one perfect asymmetrical 

 eye and the other eye of the normal pair either reduced 

 or absent, was also frequently met with under the same 

 conditions of experiment. The author claims that this is 

 the first instance of repeatedly causing, 

 by the use of chemical substances, 

 vertebrate monstrosities such as are 

 -'\. known in nature, and his results seem 

 "' to indicate that the monstrous Cyclops 

 of man and other mammals may not 

 be due to germinal variation, but to some effect of environ- 

 ment during development. 



Incidentally, the researches may also throw some light 

 upon another extremely interesting result of recent investi- 

 gation in the domain of experimental embryology. Several 

 observers, notably Spemann and Lewis, have shown that 

 in amphibian embryos the formation of the lens of the 

 eye appears to be dependent upon stimulation of the super- 

 ficial epiblast by the developing optic cup. Lewis, for 

 example, has found it possible to transplant the optic cup 

 of a frog embryo, and thereby cause the development of a 

 lens from superficial epiblast quite remote from the normal 

 lens-forming region. Stockard, however, concludes from 

 his researches on Fundulus that lens-formation does not in 

 all cases depend upon a direct stimulus from the optic 

 cup, for his abnormal Fundulus embryos sometimes showed 

 a supernumerary lens developing without any relation to 

 an optic cup. 



Why the presence of magnesium salts should cause 

 abnormal eye-development is one of the numerous 

 mysteries of biology which seem likely to remain unsolved 

 .foi- a long time to come. Experimental embryology is 

 still in its infancy, and it is too soon to expect any 

 adequate explanation of such phenomena, but we are 

 beginning to realise that the nature of the environment 

 counts for a very great deal in determining the course of 

 individual development. The most encouraging feature of 

 modern biology is, undoubtedly, the adoption of experi- 

 mental methods, and such methods bid fair to be as pro- 

 ductive in this branch of science as they have already 

 been in chemistry and physics. It would probably be too 



