AND RATIO OF TIIKIK ATOMIC WKKillTS. 79 



McLeod gauge. Then it was left at rest for twenty-four hours, :uh1 tlie vacuum 

 measured again, with the following result: 



December 11. Exhausted a[)i>aratus ; at 9 a.m., vacuum tiiree teii-milliouths. 

 Left at I'est. 



December 12. Measured vacuum left undisturbed since yestei'dav. Vacuum 

 at 10.30 A.i\i., three ten-millionths. 



It is obvious, therefoi'e, that leakage had been eliminated. 



.HI. lIVl)U0(iEN jn' NKW MKTimU. SECOND A I'I'A IJATUS. KEMAItKS. 



With this appai'atus eleven determinations were made, none being lost by 

 I'eason of accident to the apparatus, in which the probable eri'or of the determina- 

 tion of the density of a o;as so li2;ht as hydrofren was only one i>art in eiijht 

 thousand for a single experiment. The agreement of the I'esults with those of 

 series third and fourth, depending as they do on entirely different calibrations of 

 different apparatus at an inteival of months, leads me to hope that they are not 

 seriously in ei'roi'. 



It is a misfortune that it was not possible to make one or two more sei'ies oi 

 determinations, with new apparatus, or with new determinations of the capacity 

 already involved, so setting at I'est any remaining doubt. But to the 2)atience and 

 coui'age and endui'ance and powers of recuperation of a single person laboring 

 without assistance at a matter confessedly so difficult, there are limits already too 

 neai'ly reached. 



The nature of the reduction in this series is pi'ecisely the same as in the pi'e- 

 ceding, using only the altered values for capacity of the globes and of the tubes 

 connected with them. The sources of error are the same, except that leakage could 

 take place only by carelessness in constructing the fusible metal plug which closed 

 the apparatus during the exhaustion, or of the connection by which hydi'ogen was 

 admitted to the globe; which was easy to detect, and did not occur. The other 

 sources of eri-oi', also, it is thought, were avoided throughout this sei'ies of detei'mi- 

 nations. 



.">•_>. nVDWoOKN I'.V NKW METUOI). SKCOM) AIM'AUATl'S. OKSEUV A'l'lOXS AND 



KESTTLTS. 



The observations and results of the fifth series of determinations ai-e given in 

 the following table, which is in all res[)ects like that at page 74, which may be 

 consulted for ex[)lanations. The values computed for the density of hydrogen are 

 for the sea level in latitude 45°. 



