March 30, 1900.] 



SCIENCE. 



487 



cise of all these activities ; and in answer 

 to the question — What knowledge is most 

 worth ? — the answer is Science. 



" For direct self-preservation, or the 

 maintenance of life and health, the all im- 

 portant knowledge is — science. For that 

 indirect self-preservation which we call 

 gaining a livelihood, the knowledge of 

 greatest value is — science. For the due dis- 

 charge of parental functions, the proper 

 guidance is to be found only in — science. 

 For that interpretation of national life, 

 past and present, without which the citizen 

 cannot rightly regulate his conduct, the in- 

 dispensable key is — science." — economics 

 and political science. " For the most per- 

 fect production and highest enjoyment of 

 art in all its forms the needful preparation 

 is still — science. And for purposes of dis- 

 cipline, intellectual, moral, religious, the 

 most efficient study is still — science." 



It is not to be expected that these con- 

 clusions will be accepted by all to whom 

 they are addressed. I should be the last to 

 decry the importance of language study, of 

 history, art, and philosophy. I emphatic- 

 ally emphasize the importance of national 

 education in economics and political science. 

 We are sadly in need of better political 

 teachers than a majority of those who dur- 

 ing the last few years have been the leaders 

 in American politics. But I protest against 

 the implication that liberal culture is suf- 

 fering at the hands of either the active 

 workers or the leading teachers in science. 

 So long as human needs and human tastes 

 are diversified must there be corresponding 

 diversity in education. Let each of us rec- 

 ognize what is good in our neighbor, let us 

 cheerfully and cordially acknowledge the 

 value of his contribution to human welfare. 

 Let us remember that there are others be- 

 sides scientific men who are progressive, 

 and that the boundaries of knowledge are 

 ■without limit. 



Within the present century one of the 



greatest mathematicians and astronomers 

 that the world has ever known, Laplace, 

 lay on his dying bed in Paris. His last 

 words were : " Ce que nous savons est peu 

 de choses ; ce que nous ignorons est im- 

 mense. " It takes a philosopher to recog- 

 nize the immensity of his own ignorance. 

 If Laplace could use those words as he fell 

 asleep, why can we not at least follow him 

 and remain at peace with each other while 

 striving to do our share in increasing human 

 knowledge? Linguist and engineer, his- 

 torian and chemist, economist and physicist, 

 metaphj'sician and mathematician, our aims 

 radiate from a common center ; but friendly 

 and faithful as we may be to each other, our 

 ignorance will still continue to be immense. 

 W. Le Conte Stevens. 



PICTURES PRODUCED ON PHOTOGRAPHIC 

 PLATES IN THE DARK* 

 I THINK I may fairly assume that every 

 one in this theater has had his photograph 

 taken, and consequently must have some 

 idea of the nature of the process employed. 

 I have, therefore, only to add, with regard 

 to what is not visible in the process of tak- 

 ing the picture, that the photographic plate 

 is a piece of glass or such like body, coated 

 on one side by an adhesive paste which is 

 acted on by light, and acted on in a very 

 remarkable manner. No visible change is 

 produced, and the picture might remain 

 latent for years, but place this acted- on 

 plate in a solution, of, say pyrogallol, and 

 the picture appears. The subsequent treat- 

 ment of the plate with sodium hyposulphite 

 is for another purpose, simply to prevent 

 the continuance of the action when the 

 plate is brought into the light. ISTow, what 

 I purpose demonstrating to you to-night is 

 that there are other ways of producing pic- 

 tures on photographic plates than by acting 

 on them by light, and that by these other 



* Address before the Eoyal Institution of Great 

 Britain. 



