1816.] Letter to Dr. Wells respecting Dew. 111 
tirely intercepted by the internal metallic coating. In consequence 
of this there is less evaporation from the external surface of the 
coated glass. This partial explanation of the phenomena observed 
by M. Benedict Prevost is absolutely independent of the relations 
between the external and internal temperature and that of the glass 
itself. 
4. My remark on the effect of clouds in preventing, or rather 
compensating, the radiation of heat, was certainly stated too hastily 
and superticially to be in any degree comparable with the fine series 
of observations contained in your treatise on dew. ‘The attention 
which Dr. Young and yourself have paid to it constitute the whole 
of its value. 
I earnestly hope that the re-establishment of your health will 
allow you to continue your useful labours. I shall be eager to 
profit by the new discoveries which must result from them ; uniting 
in my sentiments of respect and esteem for men who, like yourself 
and Dr, Young, employ a laborious life to extend the sphere of our 
knowledge. 
Accept, Sir, the expression of these sentiments from 
Geneva, Nov. 30, 1815, E. Prevost, Professor at Geneva. 
ArticLte VII. 
Correction of a Mistake in the Essay on the Relation between the 
Specific Gravities of Bodies in their Gaseous State and the 
Weights of their Atoms. 
Tue author of the essay On the Relation between the Specific 
Gravities of Bodies in their Gaseous State and the Weights of their 
Atoms is anxious to correct an oversight which influences some of 
the numbers in the third table given in that essay (vol. vi. p. 328). 
This oversight wiil be found in the head or title of the third column 
in each table, and consists in the statement of the atom of hydrogen 
being composed of two volumes instead of one, upon which latter 
supposition the tables are actually constructed, except in the in- 
stances corrected in the third table as follows, and in a sentence in 
the first paragraph on p. 330, beginning “ This table also exhibits,” 
&c, which is to be expunged. 
