362 



Mr. J. Joly. 



bulb was quite heated in something less than four. A deduction was 

 of course made for the shield by preliminary experiments. 



I would point out that any error in Regnault's estimate of the 

 increase of specific heat of water with rise of temperature will militate 

 in a double sense against the agreement of his results with mine. For 

 this increase is assumed by Regnault in deducing, from his formula 

 for the total heat of steam, the heat of evaporation, and, as it is 

 subtr active, an error on the side of excess in his estimate of the specific 

 heat of water introduces an error on the side of insufficiency in the 

 value ascribed to X, and vice versa. Thus not alone would the quantity 

 with which I compare my results be erroneously assumed, but in 

 proportion as error exists in its value, error in the opposite direction 

 would be introduced into my results. 



I add some experiments bearing on questions of radiation error as 

 affected by extent and nature of surface exposed to the steam. They 

 are from those made on minerals, and are embodied in a paper on the 

 specific heats of minerals. (' Roy. Soc. Proc.,' vol, 41, p. 250.) 



The following table contains cases where experiments were re- 



Table I. 





W. 



w. 



h 



o 





Sp. heat. 



Limpid crystal of Barites .... 



76 '109 



1 



405 



9 



65 



100 



30 



-10923 



A portion of the same in small 



1 65 -143 



1 



195 



9- 



60 



99 



80 



-10910 













Rhomb oh edron of Iceland spar 



33 -904 



1 



156 



10 



00 



99 



76 



'20383 





33 -059 



1 



079 



13 



34 



99 



50 



-20345 



Specimen of Talc in one piece. . 



47 -445 



1 



685 



12 



•32 



100 



•25 



0-21671 



Two fragments from same hand- 



1 44 -631 



1 



568 



13 



•30 



100 



•20 



-21686 



















Specimen of Lepidolite — one 



1 42 -726 



1 



•470 



12 



•20 



100 



•20 



-20978 



















Two pieces from same hand- 



j 48 '823 



1 



•676 



12 



•38 



100 



•20 



-20967 



















Five crystals of Atnphibole .... 



57-192 



1 



•835 



12 



00 



99 



•72 



-19634 



The two largest of the five .... 



45-133 



1 



•443 



12 



•94 



100 



•30 



0-19635 



The three largest of the five . . . 



51 -309 



1 



•640 



12 



•90 



100 



•30 



-19619 



Fragments of milk-white Oli- 



1 48 -074 



1 



•546 



12 



•60 



99 



10 



-19974 



Pieces from same hand-specimen 



41 -829 



1 



•366 



11 



•60 



99 



•40 



0-19967 





20 -291 







•685 



12 



•63 



100 



•30 



20651 





17 -809 







•593 



12 



•70 



99 



•95 



20491 





20-541 







•687 



12 



•40 



99 



•90 



-20519 



Loose flakes from same hand- 



|23 -735 







•778 



13 



•80 



99 



•75 



-20466 





















