REVIEWS 321 
to make entirely clear the full value of this part of the report in a 
review, but that an invaluable service has been rendered by the authors 
will appear from the following general summary : 
Section I considers the amount of carbonic anhydride in the 
atmosphere. After discussing the effects of a permanent increase and 
decrease in the present amount of CO, in the atmosphere on plant 
and animal life, and the several theories advanced to account for the 
source of CO, to permanently augment this amount, a table showing 
the amount of CO, in 10,000 volumes of air is given. 
The arrangement of the table from left to right includes a number 
of columns under the following headings: ‘‘ Date of Observation ;” 
‘“‘ Observer;” “ Locality;” ‘‘ Number of Observations ;” “CO, in 10,000 
volumes of air, including mean, maximum, and minimum;” “ Varia- 
tion, including absolute and percentage ;” ‘‘ Author.”” ‘The tabulation 
vertically is in the order of the date of observation, beginning with the 
earliest (1797) and ending with the most recent (1897). It includes 
124 entries, the largest number of observations included in any single 
entry being the mean of 566 ; and the number of observations recorded 
in the table cover a period of 100 years. 
A perusal of the figures indicates that the earliest workers obtained 
an amount vastly too large, accredited by the authors to the methods 
used. In 1812 Thenard originated a method which yielded results 
quite close to the present ones. From this time until about the year 
1870 the average normal amount of this constituent in the atmosphere 
was given at approximately 4 in 10,000 volumes, an amount which is 
at least 25 per cent. greater than that shown at present in fresh air 
away from cities and towns, approximately 3 in 10,000 volumes. 
Section II discusses the ‘‘ Causes of Variation.” In attempting to 
review and criticise the variations in the amount of carbonic anhydride 
in the atmosphere, the authors justly appreciate the difficulties encoun- 
tered, and they state that “‘not the least of these is to correctly 
appraise and estimate the value of the evidence brought forward in 
support of the different contentions which have been raised from time 
to time in this matter.”’ Only a little study of the work of previous 
investigators is sufficient to convince one that it has taken nearly a 
century for chemists to correctly estimate the average amount of this 
constituent in the air. The figures have been reduced from roo to 
200 volumes of CO,, in case of the earliest workers, to 3 volumes 
in 10,000 volumes of air in recent investigations. Two opposite views 
