294 Dr. E. H. Cook on an JJndulatory Movement 



different powders were examined, and the number of lines in 

 a certain distance counted. Several determinations were 

 made and the mean number taken. Although every care was 

 taken to make these measurements as accurately as possible 

 and to avoid sources of error, yet, from the difficulties peculiar 

 to the case, I do not wish to pledge the absolute accuracy of 

 the numbers, but put them forward as approximate only. 

 It first became necessary to ascertain if the fineness of the 

 powder affected the number of lines in a certain length. This 

 was found not to be the case. Provided the degree of fine- 

 ness was such as to admit of the production of the lines 

 with such an amount of definiteness as sufficed for their 

 measurement, the number of lines was found to be unaltered. 

 The following tabular statement gives the results obtained. 

 The actual experiment was to count the number in a quarter 

 of an inch. These have been multiplied by 4, hence the 

 regularity of the diminution of the numbers given in the first 

 column : — 



No. of lines 

 in 1 inch. 



Substances examined. 



88. Silica (powdered sand). 



80. Magnesia alba. 



68. Chromic oxide. 



f" Antimony sulphide ; baric peroxide ; fluor spar ; cupric 

 64. J . oxide ; red lead ; lead acetate ; lead oxide ; anti- 



l mony ; sulphur ; potassium hydrogen tartrate. 

 60. Borax ; cobaltic oxide ; starch ; zinc carbonate. 



( Binoxide of manganese; baric carbonate; tricalcic 

 p-o J phosphate ; ferrous sulphide ; lead chromate ; mercuric 



1 oxide; binoxide of tin; nickel monoxide; lead car- 



( bonate ; calcic oxide. 



{Sodium hydrogen carbonate ; potassic sulphate ; potassic 

 carbonate ; mercurous chloride ; carbon ; calcic 

 hydrate. 

 ( Tannin ; salicylic acid ; rochelle salt ; ammonic sul- 

 48. < phate ; baric nitrate ; copper sulphate ; oxalic acid ; 



( sodic chloride ; succinic acid ; Epsom salts. 

 44. Alum. 



40. Chalk. 



The figures f Iron filings; baric chloride; baric sulphate; benzoic 

 weresomdefi- | acid; strontium chloride ; bismuth nitrate ; cadmium 

 nite as not to<^ nitrate ; microcosmic salt ; potassium chloride ; 

 permit count- | potassium bromide ; ammonium chloride ; ferrous 

 ing. [ sulphate ; ammonium nitrate ; pyrogallol. 



8. Effect of Mixture. — While engaged in repeating the 

 experiments, in order to confirm the numbers, it was found 

 that a particular sample of calcic oxide gave 48 lines to the 

 inch instead of 56, as given in the table. Upon examining 



