268 MR. E. H. GRIFFITHS ON THE LATENT 
I think the preceding summary fairly represents the remarks of WINKELMANN on 
the determinations at low temperatures.* 
I will now add some remarks of my own. 
REGNAULT was compelled to limit the duration of these experiments as much as 
possible, otherwise his correction for the loss or gain by radiation, etc. (which was at 
best but a somewhat uncertain one) became large as compared with the other 
magnitudes to be measured. The average length of an experiment was about five 
minutes, though in one or two extreme cases it extended to 11 minutes; in this 
time he evaporated about 5°3 grams of water, and thus he was compelled to reduce 
the pressure in the condenser very considerably below the pressure of saturated 
vapour at the temperature of the calorimeter. He was, therefore, unable to diminish 
the sources of error (subsequently dwelt upon by WINKELMANN) in the manner he 
might have done had he not been thus limited in time. REGNAULT, referring to the 
difference between the pressure in the condenser and in the calorimeter, writes as 
follows : “‘ La différence entre les deux tensions doit méme étre assez grande; car 
pour que l’expérience se fasse dans des conditions favorables d’exactitude ; il faut que 
la distillation soit assez rapide, afin que la correction e ne soit jamais qu’une fraction 
trés-petite de ¢) — 4.” 
Again, another matter of importance is the thermometry. On p. 692 (ibid.) he 
says: ‘‘ Les thermométres 4 mercure des calorimétres ont étés gradués avec le plus 
grand soin, un degré centigrade occupe sur la tige du thermométre 
du calorimétreC. . . . . 18°°7620; par suite 1° vaut 0°:053283. 
= On ¢ = » 5 LA EROS I ODESSA. 
93 
Il est facile d’apprécier avec certitude le dixiéme des divisions, c’est-A-dire 345 de 
deoré centigrade dans les lunettes horizontales avec lesquelles on observe les 
thermométres.” 
The only other reference is on p. 707, where he remarks that he reduced the 
readings from the mercury to the air scale by means of the table given on p. 239 of 
his paper ‘‘ De la mesure des Températures.”{ I have searched the paper throughout 
for some indication as to the thermometers actually used, in the hope that I might 
be able to identify them with some one of those of whose comparison with the air 
thermometer he gave an account in another paper; but the above are the only 
references to the thermometry that I have been able to find. Had a direct com- 
parison between these thermometers and the air thermometer been made, it is most 
probable that Recnautt would have mentioned it; we may, therefore, assume that, 
* Had not RecNauLT measured the temperature of the evaporating water by means of the vapour 
pressure in the condenser, the above objections would lose their force. 
+ ‘Mémoir. de l’Acad.,’ vol. 21, 1847, p. 716. 
t ‘ Mémoir. de l'Institut,’ vol. 21, p. 220 
