3o8 POPULAR SCIENCE MONTHLY. 



be along the lines of possible development that would be too 

 commonplace and altogether out of keeping with the ideal of the 

 greatness of the future achievements of mankind. They must 

 necessarily assume that what is brought forth hereafter will be 

 so far in advance of what we now know of as to be revolutionary 

 in its character, and so much so, in fact, as to consign to the scrap 

 heap the most perfect devices of the present time. Some of the 

 means by which these results are to be attained are not capable of 

 accomplishing such wonders ; others, while of great theoretical 

 possibilities, are surrounded by certain practical difficulties so 

 well understood at the present time that we can almost with cer- 

 tainty say that they will never realize the dreams that are based 

 upon them. The remainder are problems that can be solved to- 

 day, and would be if it were not for the fact that it is by no 

 means certain that their solution would be of any practical value. 

 The improbability of ever realizing a substantial gain by the 

 solution of many of the problems upon which jDrophecies as to 

 the wonders of the future are based is fully appreciated by many 

 of those who have given the subject careful consideration ; but 

 those who dream of the revolutionary character of future inven- 

 tion never take note of such things. 



Nearly all those who succumb to the fascination of meditating 

 upon the changes that may be wrought by inventive genius in 

 days to come follow the same line of thought. The problems 

 upon the solution of which their fancy paints its pictures are 

 always the same, although some contemplate the whole category, 

 while others only dwell upon a portion thereof. These problems 

 are aerial navigation, the development of electric energy direct 

 from coal or some other equally cheap substance, and the utiliza- 

 tion of the various forces of Nature, such as solar heat, tide and 

 wave motion, and wind currents. Of these, aerial navigation is 

 supposed to be by far the most important, obtaining electricity 

 direct from coal and the others following along in the order in 

 which they are given above. 



As to the utilization of solar heat, tides, wave motion, and 

 wind currents, it can be truthfully said that they could be util- 

 ized at the present time if it were considered profitable to do so. 

 The energy of wind currents, as every one knows, is made avail- 

 able on a very extensive scale, but always in small units, and this 

 fact alone shows that it can not compete with the steam engine, 

 which, according to the prophets, it is sure to supersede. The 

 energy of tides and wave motion is also utilized to some extent, 

 and solar engines have been made from time to time. 



It can not be said that these unlimited sources of energy are 

 not brought into the service of man because of our inability to 

 devise apparatus with which to harness them successfully, for, as 



