Manchester Memoirs, Vol. Ivii. (19 13), No. 10. 5 



The fact that mention is made of 

 Deutoxide of Hydrogen (Hydrogen peroxide HjOa), 

 which was only discovered by Thenard in 18 18, will 

 compel us to date the handwriting not earlier than that 

 year. On the other hand, it can be shown by comparison 

 that this table was a draft for the last table published by 

 Dalton in 1827. It is therefore evident that it was 

 written between 18 18 and 1827. 



As Sir Henry Roscoe has reproduced in his ' New 

 view of the Origin of Dalton's atomic theory ' the first 

 draft of the atomic figures, the original of which belongs 

 to this Society, I thought it would be interesting to see 

 the table in its final form. 



With the name of Dalton is closely connected that of 

 William Henry. William Henry, the son of Thomas 

 Henry, who was the Secretar)' of the Literary and 

 Philosophical Society, and its President from 1807 to 18 16, 

 studied medicine and became Physician to the Manchester 

 Infirmary. Like his father, he was deeply interested in 

 Chemistry. In this field, the law^ named after him, 

 communicated by him to this Society in 1803, has cer- 

 tainly to be accounted one of the impulses actuating Dalton 

 in his atomic investigations. Henry also resembled 

 his father in that he was a successful chemical manufac- 

 turer. The following letter shows him vacillating between 

 scientific pursuits and practical progress : — 



Manchester, 



i8th August, 1817. 

 My Dear Sir, 



It is impossible that I can feel otherwise than 

 highly gratified by your friendly letter which has 

 this morning reached me, and by the flattering sug- 

 gestion which it contains. To be thought worthy, 



1 Henry's law states that the volume of a gas dissolved by a definite 

 volume of a liquid is independent of the pressure. 



