36 
Here follows the table of the relative weights of the 
atoms :• 
TABLE 
Of the relative weights of the ultimate particles of gaseous and 
other matters. 
Hydrogen 1 
Azot 4‘2 
Carbone A3 
Ammonia 5' 2 
Oxygen 5*5 
Water 6‘5 
Phosphorus 7*2 
Phosphurretted hydrogen 8*2 
Nitrous gas 9'3 
Ether 9*6 
Gaseous oxide of carbone 9‘8 
Nitrous oxide 13*7 
Sulphur 14'4 
Nitric acid 15*2 
Sulphuretted hydrogen 15*4 
Carbonic acid 15"3 
Alcohol 15*1 
Sulphureous acid 19*9 
Sulphuric acid 25 '4 
Carburetted hydrogen from 
stagnant water 6’3 
Olefiant gas 5‘3 
In the 2nd part of his New System of Chemical Philo- 
sophy, published in 1810, Dalton points out under the 
description of each substance the experimental evidence 
upon which its composition is based, and explains, in some 
cases, how he arrived at the relative weights of the ultimate 
particles in question. Between the years 1805 and 1810, 
however, considerable changes had been made by Dalton in 
the numbers ; the table found in the first part of the New 
System being not only much more extended, but in many 
cases the numbers differing altogether from those given in 
the first table published in 1805. It is therefore, unfor- 
tunately, to a considerable extent now a matter of conjecture 
how Dalton arrived at the first set of numbers. All we 
know is that it was mainly by the consideration of the 
composition of certain simple gaseous compounds of the 
elements that he arrived at his conclusions, and in order 
that we may form some idea of the data he employed we 
must make use of the knowledge which chemists at that 
time (1803-5) possessed concerning the composition of the 
more simple compound gases. 
As I can find no record of any explanation of these early 
numbers I venture to bring the following attempt to trace 
their origin before the Society to whom we owe their first 
publication. 
The first point to ascertain, if possible, is how Dalton 
