224 Lord Rayleigh on the Scientific Work of Tyndall. [March 16, 



following Tyndall, we hold a spirit lamp under the track of the light 

 from the electric lamp, the dark spaces, resulting from the combus- 

 tion of the dust, have all the appearance of smoke. 



In confined and undisturbed spaces the dust settles out. I have 

 here a large flask which has been closed for some days. If I hold it 

 to the lamp, the track of the light, plainly visible before entering 

 and after leaving the flask, is there interrupted. This, it will be 

 evident, is a matter of considerable importance in connection with 

 organic germs. 



The question of the spontaneous generation of life occupied 

 Tyndall for several years. He brought to bear upon it untiring 

 perseverance and refined experimental skill, and his results are those 

 now generally accepted. Guarding himself from too absolute state- 

 ments as to other times and other conditions, he concluded that under 

 the circumstances of our experiments life is always founded upon 

 life. The putrefaction of vegetable and animal infusions, even when 

 initially sterilised, is to be attributed to the intrusion of organic 

 germs from the atmosphere. 



The universal presence of such germs is often regarded as a 

 hypothesis difficult of acceptance. It may be illustrated by an ex- 

 periment from the inorganic world. I have here, and can project 

 upon the screen, glass pots, each containing a shallow layer of a 

 supersaturated solution of sulphate of soda. Protected by glass 

 covers, they have stood without crystallising for forty-eight hours. 

 But if I remove the cover, a few seconds or minutes will see the 

 crystallisation commence. It has begun, and long needles are in- 

 vading the field of view. Here it must be understood that, with a 

 few exceptions, the crystalline germ required to start the action must 

 be of the same nature as the dissolved salt ; and the conclusion is 

 that small crystals of sulphate of soda are universally present in the 

 atmosphere. 



I have now completed my task. With more or less success I 

 have laid before you the substance of some of Tyndall's contributions 

 to knowledge. What I could not hope to recall was the brilliant 

 and often poetic exposition by which his vivid imagination illumined 

 the dry facts of science. Some reminiscence of this may still be 

 recovered by the reader of his treatises and memoirs; but much 

 survives only as an influence exerted upon the minds of his contem- 

 poraries, and manifested in subsequent advances due to his inspiration. 



[Rayleigh.] 



