152 Science applied to the detection of crime. 



are now sources of very large income to those com- 

 panies. Those substances yield great quantities of 

 salts of ammonia, the beautiful aniline dyes, paraffin, 

 benzene, napthaline, alizarine, and other valuable 

 products, Glycerine also, which formerly was a most 

 offensive waste product in soap-making, is now puri- 

 fied and used, to an extent of twenty millions of 

 pounds anually, for a great number of purposes; as an 

 emollient for the skin ; as a source of nitro-glycerine 

 and dynamite, used in blasting rocks, in warfare, &c. 

 The immense beds of native sulphide of iron also, 

 notably those of Tharsis and Rio Tinto in Spain, 

 and of many other places, are now utilized, literally 

 in millions of tons, for the production of sulphur, 

 copper, oxide of iron, &c. A long list of instances of 

 this class might be adduced if it were necessary, some 

 of them of very great importance.* 



The promotion of morality by enabling us to detect 

 crime, is one of the smaller influences of scientific 

 research, and may be referred to as a set-off against 

 the bad uses sometimes made of scientific knowledge. 

 The telegraph is very commonly employed to assist 

 in tracking and capturing criminals. Photography is 

 also largely used in our goals as a means of recog- 

 nising offenders. 



Knowledge of science conduces also to self-discipline 

 and self-mastery, it tends to bridle our vicious 

 passions by making known to us the penalties which 

 must be paid for their indulgence ; it limits our self- 

 will by shewing us that we must respect and obey the 



* See " Waste Products and Undeveloped Substances," by P. W. Simmonds. 



