LEEOT C. COOLEY. 113 



or principle. Boyle had himself noticed that the actual 

 results of experiments were not in exact accordance 

 with the law which he had formulated ; others had 

 witnessed the same discrepancies, but the deviations, 

 which seemed to increase as the pressure became greater, 

 were by him and them attributed to errors in their ex- 

 periments. These deviations from the law were exhib- 

 ited in a marked degree in a more extended series of ex- 

 periments made by Sulzer in 1753. Nevertheless he also 

 regarded them as effects of imperfect manipulation. It 

 may be said that Sulzer added no new method ; that he 

 contributed nothing to the forms of apparatus, and that 

 his experiments are worthy of special notice only be- 

 cause they surpassed those of his predecessors in the 

 amount of pressure applied. In theirs it had not exceed- 

 ed four atmospheres ; in his it was augmented to eight. 



EOBITSTSOiN". 1 



Sulzer' s experiments were afterward repeated by Rob- 

 inson with precautions against what he regarded as the 

 chief sources of error. These were, first of all, the pres- 

 ence of other gases, notably of the vapor of water in 

 the air operated upon, and then, also, the presence of 

 impurities such as bismuth and tin, together with air in 

 the mercury employed for pressure. He therefore care- 

 fully removed the vapor of water from the air by desic- 

 cation, and the air from the mercury by boiling, while 

 by using the same mercury for his experiments as that 

 employed in his standard barometer he hoped to elimi- 

 nate the effects of any baser metals which might be 

 present. 



The following table contains the results of his experi- 

 ments on dry air. The first column gives the densities 



1 Encyclopaedia Britannica 8th ed., vol. xvi. 

 Encyclopaedia Metropolitana. 



System of Mechanical Philosophy, vol. iii., p. 637. 



65 



