742 THE POPULAR SCIENCE MONTHLY. 



time and energy to the actual advancement of knowledge. iJ^ot that 

 I would complain of the association sanctioned by common parlance. 

 A sound knowledge of at least the principles of general physics is 

 necessary to the cultivation of any department. The predominance 

 of the sense of sight as the medium of communication with the outer 

 world brings with it dependence upon the science of optics ; and there 

 is hardly a branch of science in which the effects of temperature have 

 not (often without much success) to be reckoned with. Besides, the 

 neglected border-land between two branches of knowledge is often 

 that which best repays cultivation, or, to use a metaphor of Maxwell's, 

 the greatest benefits may be derived from a cross-fertilization of the 

 sciences. The wealth of material is an evil only from the point of view 

 of one of whom too much may be expected. Another difficulty incident 

 to the task, which must be faced but can not be overcome, is that of 

 estimating rightly the value, and even the correctness, of recent 

 work. It is not always that which seems at first the most important 

 that proves in the end to be so. The history of science teems with 

 examples of discoveries which attracted little notice at the time, but 

 afterward have taken root downward and borne much fruit upward. 



One of the most striking advances of recent years is in the pro- 

 duction and application of electricity upon a large scale — a subject to 

 which I have already had occasion to allude in connection with the 

 work of Sir W. Siemens. The dynamo-machine is, indeed, founded 

 upon discoveries of Faraday now more than half a century old ; but 

 it has required the protracted labors of many inventors to bring it to 

 its present high degree of efficiency. Looking back at the matter, 

 it seems strange that progress should have been so slow. I do not 

 refer to details of design, the elaboration of which must always, I 

 suppose, require the experience of actual work to indicate what parts 

 are structurally weaker than they should be, or are exposed to 

 undue wear and tear. But, with regard to the main features of the 

 problem, it would almost seem as if the difficulty lay in want of faith. 

 Long ago it was recognized that electricity derived from chemical 

 action is (on a large scale) too expensive a source of mechanical 

 power, notwithstanding the fact that (as proved by Joule in 1846) 

 the conversion of electrical into mechanical work can be effected with 

 great economy. From this it is an evident consequence that electricity 

 may advantageously be obtained from mechanical power ; and one 

 can not help thinking that, if the fact had been borne steadily in mind, 

 the development of the dynamo might have been much more rapid. 

 But discoveries and inventions are apt to appear obvious when re- 

 garded from the stand-point of accomplished fact, and I draw attention 

 to the matter only to point the moral that we do well to push the 

 attack persistently when we can be sure beforehand that the ob- 

 stacles to be overcome are only difficulties of contrivance, and that we 

 are not vainly fighting unawares against a law of Nature. 



