THE SCIENTIFIC WORK OF TYNBALL. 659 



years of labor within these walls lie ranged over a vast field, and 

 accumulated results of a very varied character, important not 

 only to the cultivators of the physical sciences, but also to the 

 biologist. All that I can hope to do is to bring back to your 

 recollection the more salient points of his work, and to illustrate 

 them where possible by experiments of his own devising. 



In looking through the catalogue of scientific papers issued 

 by the Royal Society, one of the first entries under the name of 

 Tyndall relates to a matter comparatively simple, but still of 

 some interest. It has been noticed that when a jet of liquid is 

 allowed to play into a receiving vessel, a good deal of air is some- 

 times carried down with it, while at other times this does not 

 happen. The matter was examined experimentally by Tyndall, 

 and he found that it was closely connected with the peculiar 

 transformation undergone by a jet of liquid which had been pre- 

 viously investigated by Savart. A jet as it issues from the nozzle 

 is at first cylindrical, but after a time it becomes what the physi- 

 ologists call varicose; it swells in some places and contracts in 

 others. This effect becomes more exaggerated as the jet descends, 

 until the swellings separate into distinct drops, which follow one 

 another in single file. Savart showed that under the influence of 

 vibration the resolution into drops takes place more rapidly, so 

 that the place of resolution travels up closer to the nozzle. 



Tyndall's observation was that the carrying down of air re- 

 quired a jet already resolved into drops when it strikes the liquid. 

 I hope to be able to show you the experiment by projection upon 

 the screen. At the present moment the jet is striking the water 

 in the tank previous to resolution into drops, and is therefore 

 carrying down no air. If I operate on the nozzle with a vibrat- 

 ing tuning fork, the resolution occurs earlier, and the drops now 

 carry down with them a considerable quantity of air. 



Among the earlier of Tyndall's papers are some relating to ice, 

 a subject which attracted him much, probably from his moun- 

 taineering experiences. About the time of which I am speaking 

 Faraday made interesting observations upon a peculiar behavior 

 of ice, afterward called by the name of regelation. He found 

 that if two pieces of ice were brought into contact they stuck or 

 froze together. The pressure required to produce this effect need 

 not be more than exceedingly small. Tyndall found that if frag- 

 ments of ice are squeezed they pack themselves into a continuous 

 mass. We have here some small ice in a mold, where it can be 

 subjected to a powerful squeeze. The ice under this operation 

 will be regelated, and a mass obtained which may appear almost 

 transparent, and as if it had never been fractured at all. The 

 flow of glaciers has been attributed to this action, the fractures 

 which the stresses produce being mended again by regelation. I 



