THE METHOD OF SCIEXCE 43 



necessary quantity as required. But a primitive builder will 

 fetch his materials as he wants them, obtaining more and 

 more until the building is finished, without any preliminary 

 survey of the quantity required. Modern industry makes use 

 of statistical surveys and cost analysis. Only a fe^v years ago 

 such aids to operation ^vere unknots n. Such matters have no 

 relation to the technical skill of the craftsman; the builders 

 of the Pyramids and the goldsmiths ^vho wrought the coffin 

 of Tutankhamen ^vere craftsmen of superb skill, but they 

 probably did little calculating before they started work. 



Technology has usually proceeded by trial and error. The 

 practice of photography, for instance, preceded any knowl- 

 edge of the theory of the photographic process. Photographic 

 materials w^ere made by trial, and to this day the making of 

 photogiaphic materials is in advance of the understanding of 

 the basic science of the subject. Advances in photographic 

 science have pro\'ided a "^vorking theory of the light sensi- 

 tivity of photographic materials, of ^vhat happens to them 

 during exposure, and of ^vhat happens to them during de- 

 velopment. But the relationship bet^veen the operations of 

 making the photographic emulsion and the properties of the 

 resultant emulsion is not yet understood. Only a ie^v years 

 ago practically nothing was kno^vn of the "^vay in "vvhich cer- 

 tain dyes sensitize silver bromide in photographic emulsions 

 to the regions of the spectrinn which the dyes absorb. The 

 matter is being elucidated, but ignorance of it did not pre- 

 vent our discovering great numbers of dyes and applying 

 them to the sensitizing^ of silver bromide. 



There comes a point in technology, however, where prog- 

 ress is sloAV or even stops for lack of knowledge of the funda- 

 mental science. Progress in photogiaphy has been greatly 

 accelerated by our luiderstanding the physical chemistry un- 

 derlying the photographic process. 



Progress in engineering is dependent to a very great extent 

 on fundamental physics, on ^vhich all engineering is based. 

 But the invention of the steam engine ^vas not dependent 

 upon the understanding of Ne^vton's work, nor was the de- 



