752 



THE POPULAR SCIENCE MONTHLY 



the nature of that agent as well as of 

 dynamic philosophy so Dr. Lardner 

 went over the ground of physics in his 

 five-years' lectures in this country in 

 complete ohliviousness of the new point 

 of view that had even then heen as- 

 sumed hy investigators of his own and 

 other countries. 



But Prof. Tyndall belongs to the 

 later era: he has done his share in 

 bringing it about, and is among its 

 ablest representatives. Besides his 

 original contributions to the more re- 

 cent phases of science, by his genius 

 for lucid and eloquent statement he 

 has done perhaps more than any other 

 man to put the new doctrines into 

 popular and attractive form. In his 

 classical volume entitled "Heat as a 

 Mode of Motion," he takes the point 

 of view definitely assumed by Eum- 

 ford, and has worked out the science 

 of thermotics on a modern basis and in 

 harmony with the later views of the 

 nature of force or energy. As all who 

 have read his works are aware, Tyndall 

 is more than a mere specialist ; he is 

 a broad thinker a philosopher of sci- 

 ence. JSTo man is more painstaking or 

 scrupulous in elaborating isolated facts 

 with accuracy, but that does not con- 

 tent him, nor is he satisfied with the 

 narrow theories that have been ap- 

 plied to them; but he strives after 

 those wider and deeper explanations by 

 which diverse phenomena are brought 

 into harmonized relations. The vari- 

 ous physical forces are interesting to 

 him in their pure phenomenal work- 

 ings, but they have a larger interest as 

 clews to the constitution of matter. 

 Physics has two great departments. 

 Molar Physics treats of the movements 

 and mechanical properties of masses, 

 as the revolutions and attractions of 

 the celestial orbs, or the laws of motion 

 in terrestrial bodies. Molecular Phys- 

 ics, on the other hand, deals with the 

 subtler forces of magnetism, heat, light, 

 electricity, and affinity, by which the 

 inner nature of matter is affected and 



its profoundest changes brought about. 

 It is this division or aspect of physics 

 that has mainly engaged the attention 

 of Prof. Tyndall. His first scientific 

 reputation was made by researches in 

 the field of magnetism, and his origi- 

 nal papers upon this subject have re- 

 cently appeared in an elaborate volume. 

 Glacial phenomena have also been fa- 

 vorite objects of study with him. In- 

 volving as they do the molecular muta- 

 tions of water, through the vaporous, 

 liquid, and solid conditions, on a grand 

 and impressive scale, they afford a fine 

 exemplification of the play of molecu- 

 lar forces of which Prof. Tyndall has 

 availed himself, both to extend our 

 knowledge of the subject and to enlist 

 the interest of the public in some of 

 the most beautiful and wonderful oper- 

 ations of Nature. The first book by 

 which Prof. Tyndall became widely 

 known was his "Glaciers of the Alps." 

 now long out of print ; and his latest 

 work, to be immediately published, is 

 on the "Forms of "Water," in clouds, 

 rain, rivers, ice, and glaciers. Much 

 of his time during the last dozen years 

 has been devoted to the revision and 

 extension of his early opinions upon 

 these subjects. The courses of lectures 

 which he is to give in this country will 

 be eminently valuable as reflecting the 

 latest views that have been formed in 

 a field of science that has undergone 

 a great change within a recent period. 

 We shall be able to listen to the au- 

 thentic teachings of a master in sci- 

 ence, and one who is, moreover, a mas- 

 ter in the art of popular exposition. 



THE PRESIDENTIAL ADDRESSES. 



Ijt our present number will be 

 found the addresses of the presidents 

 of the two scientific associations held 

 in August, the one in Dubuque, Iowa, 

 and the other in Brighton, England. 

 They are entitled to consideration 

 from the positions of their respective 

 authors, the weight and dignity of the 

 bodies addressed, and the interest of 



