16 POPULAE SCIENCE. 



ated,the number of men to whom the unravelling of truth for 

 its own sake is possible will be comparatively few. The num- 

 ber, however, will be probably commensurate with the num- 

 ber of intellects strong enough to be turned advantageously 

 in this direction. The belief is very common, that discovery 

 and invention are only two developments of one and the same 

 faculty, but in inferior degree. An opinion prevails that dis- 

 coverers are by necessity inventors ; men who, looking down 

 on human needs, might, if they would only condescend, turn 

 their discoveries to profitable use. This opinion does not 

 appear to be borne out by facts. The faculty of invention 

 would appear to be different from that of discovery, and few 

 experimental discoverers could be predicated to their utilita- 

 rian issues by aid of theory alone. Of this some remarkable 

 instances may be cited. The theoretical prediction made by 

 Dr. Lardner, that ships steam-propelled would never be able 

 to .cross the Atlantic, has been often quoted, and is popularly 

 known. Not so well known is the fact that a lecture was 

 once delivered at the Royal Institution to prove that elec- 

 tricity could never be used for telegraphic purposes save for 

 very inconsiderable distances, the maximum specified distance 

 being, I believe, no more than eighteen miles. 



It is curious to reflect on cases in which Science has fre- 

 quently come to the aid of utilitarian man just when wanted 

 so soon, indeed, as utilitarian man has deliberately sought 

 her aid. Some remarkable examples of this are afforded by 

 the history of the great French Revolution. Much fighting 

 had then to be done, as readers need not be informed; but 

 fighting needs gunpowder, gunpowder needs saltpetre, and 

 up to the period of the revolution almost all the saltpetre of 

 commerce had been imported from India. True, the Italians 

 were aware that saltpetre occasionally forms in caves and 

 tombs ; the fact is stated by the Italian writer Tartalea. This 

 does not invalidate the fact, that before the French Revolu- 

 tion nearly all the saltpetre of commerce was brought from 



