SCIENTIFIC NOTES. 29 



freezing; cold alone will not destroy it. Animal life of the higher 

 types is unable to withstand for any length of time temperatures 

 much below 50°. The simpler forms of life, such as seeds, etc., 

 seem to resist any low temperature yet applied to them. This fact 

 has led Lord Kelvin and others to suspect that life came to the earth 

 from distant bodies being brought through the intense cold of inter- 

 stellar space in meteorites or driven in very simple cell form by 

 radiation pressure. However this may be we must admit that the 

 great preponderance of life upon the earth has existed since the 

 temperature fell below the boiling point and will cease to exist when 

 the temperature falls very far below the freezing point. We live 

 then in a small part of the scale of a vast thermometer extending 

 from 273° below zero (absolute zero) to perhaps 7000° above zero, 

 the temperature of the sun. So if our earth has cooled down from 

 the upper limit or anywhere near it and is to finally reach the cold- 

 ness of interstellar space, life is an exceedingly fleeting thing. 

 Amongst all of the inconceivably large number of visible stars, to 

 say nothing of the ones not shining by their own light, and the dark 

 stars which we know to exist, it is unreasonable to suppose that the 

 earth is the only body amongst all these on which are the conditions 

 necessary for the support and development of some form of life. 

 Many must have had these, many have them now and no doubt many 

 have yet to reach the temperature where life may be possible. That 

 this life is like our own is not necessary; it may be, of course, that 

 development would proceed along very different lines, so that to 

 admit conditions on Mars favorable to the support of life is not at 

 all the same thing as to say that there are beings there eagerly wait- 

 ing for the scientists of this planet to arouse themselves and begin 

 interplanetary communication. 



It was van der Waals who called attention to the similarity of 

 properties of different substances in enunciating the law of Corre- 

 sponding States, which is to the effect that all substances have iden- 

 tical properties so far as the relations amongst temperature, pressure, 

 and volume are concerned. All liquids if heated in an open vessel, 

 provided they do not undergo decomposition, boil at definite tem- 

 peratures which change with the pressure. If, however, a liquid be 

 heated in a closed vessel the evaporation increases the pressure, so 

 that the boiling point is raised, and increasing temperature increases 

 the evaporation and the pressure, so that the boiling point is never 

 reached. This continues until a certain temperature, depending on 

 the liquid, is reached, when the liquid changes into vapor without 



