C. ELECTRICITY, LIGHT, HEAT, AND SOUND. 45 



of crystals could be appreciated, with all their peculiarities. 

 He thinks, however, that while this period is sufficient for the 

 production of a strong and distinct impression upon the reti- 

 na, a smaller interval will suffice for many purposes, and that 

 four billionths of a second, and, perhaps, even a shorter time, 

 may be sufficient. This, according to the Professor, is not so 

 wonderful, if we accept the doctrine of the undulatory theory 

 of lio-ht, as, according to it, in four billionths of a second 

 nearly two and a half millions of the mean undulations of 

 light reach and act upon the eye. 4X>, September, 1871,155. 



INFLUENCE OF LIGHT ON PETROLEUM. 



According to recent researches, petroleum, when exposed 

 to solar light, absorbs oxygen and changes it into ozone, al- 

 though this does not combine with the oil, the ozone remain- 

 ing free, and oxidizing every thing with which it comes in 

 contact. Petroleum oils impregnated with ozone have a to- 

 tally altered smell, burn with more difficulty, and attack the 

 cork stoppers of the vessels very strongly. If the vessels are 

 of glass, their color exercises much influence upon the absorp- 

 tion of oxygen by the petroleum. Thus petroleum oils, when 

 exposed in white glass to solar and daylight, become yellow 

 and impregnated with ozone, assuming a greater specific 

 gravity, and losing their ready combustibility. This is said 

 to be especially the case with American petroleums. The 

 practical inference may therefore be deduced that petroleum 

 intended for burning should be kept in stone or metal vessels, 

 or, if in glass, protected as much as possible against the influ- 

 ence of daylight, 13 (7, 1871, August 11,1151. 



SPECTPvUM ANALYSIS OF BLOOD. 



Mr. H. C. Sorby, well known for his skill in spectrum anal- 

 ysis, in reply to certain expressed doubts, maintains that 

 there is no better way of determining the existence of blood, 

 -under any given circumstances, than its examination by 

 means of the spectroscope. The absorption bands are perfect- 

 ly distinct and well defined, and, indeed, so marked that a 

 stain containing less than one hundredth of a grain can be 

 recognized even after the lapse of fifty years. In this asser- 

 tion he does not wish to be understood as stating that human 

 blood can be thus definitelv distinguished from that of other 



