tlie Temperature of Liquid Hydrogen on Seeds. 



365 



of heat observed by Pictet appearing to be due, not so much to the 

 materials themselves, as to the air contained in their interstices. 

 Good exhaustion in the ordinary vacuum vessels used in low tempera- 

 ture work, reduces the influx of heat to one-fifth of what is conveyed 

 when the annular space of such double-walled vessels is filled with 

 air/'* 



It is to be noticed that in Professor Dewar's first experiment, the 

 seeds were practically in a vacuum. It is obvious from what has been 

 quoted above, that this would help them to retain their heat. Any 

 hesitation in accepting the results of the experiment on this ground 

 is however swept away by the second experiment in which the seeds 

 with absolutely no protection at all, were actually soaked in liquid 

 hydrogen for six hours. The extremity of caution can hardly resist 

 the conclusion that they must have been brought to the same tem- 

 perature. 



Professor Dewar finds "that silica, charcoal, lampblack, and oxide 

 of bismuth, all increase the insulation to four, five and six times that 

 of the empty vacuum space." It might possibly be worth while to 

 try how far a packing of small air-dry seeds would compare, say with 

 charcoal. And this would in some degree be a measure of the thermal 

 transparency of seed structures. 



Professor Dewar suggested to me that I should supplement this 

 statement by some remarks on the physiological bearing of the ex- 

 periment. This has already been discussed by Messrs. Brown and 

 Escombe, and there is perhaps little of moment to add to their con- 

 clusions. 



The real interest of the whole investigation obviously lies in the 

 question how far it modifies our conceptions of the nature and pro- 

 perties of living matter. Protoplasm, whatever its source, has physical 

 properties and an ultimate chemical composition which are practically 

 uniform. This uniformity, however, overlies a potential diversity 

 which is not to be measured. Such diversity cannot be accounted for 

 by any purely physical conceptions, as physical conceptions are 

 understood. 



We not merely know the ultimate constitution of protoplasm, but 

 we also know a good deal about its proximate constitution. Yet the 

 properties of living protoplasm are very far removed from the mere 

 sum of those of its constituents, and no light can be derived with 

 respect to them in this direction. And what we know about the con- 

 stituent bodies themselves is at present not a little obscure. They 

 belong, as it were, almost to the fringe of possible chemistry and 

 almost elude the methods of chemical research. But they, complex as 

 they are, are not themselves protoplasm. Their cumbrous molecules 

 are built up and broken down by ordinary chemical processes. They 



* " On Liquid ^ir as an Analytic Agent," ' Roy. Inst.,' Apr. 1. 1898, pp. 7 and 8. 

 VOL. LXV. 2 E 



