PROFESSOR TYNDALL. 127 



now to be supplied. Their production has necessarily, and as a guarantee 

 of their reliability, to be the joint product of several independent workers, 

 and those names which must ever remain memorably associated with their 

 forging, are those of Professor Tyndall and Messrs. Dallinger and Drysdale. 

 As a humble labourer at the eleventh hour only, seeking for and obtaining 

 evidence of an independent character corroborative of the important results 

 achieved by the foregoing authorities, the author of the present volume is, 

 as presently shown, also in a position to subscribe his name as an additional 

 witness for the panspermists. 



Commencing with the achievements of Professor Tyndall in this special 

 field of research, it has first to be related that his earliest association with 

 the subject of spontaneous generation was the result of a happy accident. 

 In the course of those physical investigations for which his name is so justly 

 famous, he happened, while experimenting on the subject of radiant heat 

 in relation to the gaseous form of matter, to require air that was completely 

 free from all extraneous or floating matter, however fine. The passage 

 of the same through alkalis, acids, alcohols, and ethers, was found insufficient 

 to produce the purity desired ; but on the other hand, air filtered through 

 cotton-wool, air kept free from agitation sufficiently long to allow the floating 

 particles to subside, air in a calcined state, or obtained from the deeper 

 cells of the human lungs, proved to be effectually cleansed from all such 

 floating substances and to be in every way suited for the purposes required. 

 A delicate and certain method of testing atmospheres to ensure their 

 requisite purity was also devised by Professor Tyndall. This ready test 

 was found to be presented by a concentrated beam of the oxyhydrogen or 

 electric lamp. Surrounding objects being in darkness, such a beam thrown 

 across the ordinary atmosphere revealed its track in a similar manner, but 

 to a still more intense degree, as a sunbeam shining through a minute 

 aperture of a closed window-shutter ; wherever it passed it either threw up 

 vividly distinctly moving dust, or presented a turbid or foggy aspect, through 

 the reflection or scattering of light of the myriads of invisibly minute 

 particles with which the same air was laden. Passing a similar beam 

 through air purified in either of the manners above recorded, no such 

 interruption of its course occurred, and from one end to the other of the 

 traversed space its route was dark, and entirely indistinguishable from the 

 surrounding and unilluminated atmosphere. 



It presently occurred to Professor Tyndall that the important results 

 obtained by Schwann, Schroder, and Pasteur, and other notable pansper- 

 mists, concerning the sterility of certain exposed infusions, were intimately 

 associated with those pure and moteless optic conditions of the atmosphere 

 last described. Put to the test, this inference was verified beyond his most 

 sanguine expectations. The ordinary infusions of turnip, hay, and other 

 organic substances were prepared in tubes, and after boiling left to their 

 fate in carefully closed chambers of ingenious construction, whose air con- 

 tents, after two or three days allowed for subsidence, were shown by the 



