86 Dr. Thomson’s Account of the [Fes. 
before. He relates the various improvements made in these 
machines in France and Italy, and particularly by Mr. Cuth- 
bertson at Amsterdam, who brought that kind of machine to 
erfection, and still continues to make them in Poland-street, 
ondon. 
8. On the Degree of Salubrity of Common Air at Sea, com- 
pared with that of the Sea Shore, and that of Places far removed 
from the Sea. Phil. Trans. 1780, p. 354.—He tried air by 
Fontana’s method at the mouth of the Thames, and afterwards 
at Ostend, and in various parts of the Netherlands, France, and 
Germany. He concluded from his cbservation, that the air is 
purer at sea than over land, and purer on the sea shore than at a 
distance from the ocean. But these inferences were made from 
too lmited a number of experiments. Indeed only one, or at 
most two experiments were made at sea. It is now perfectly 
established that there is no difference whatever between air at 
sea and air atland. The supposed differences originated entirely 
from imaccuracies in the mode of making the experiments, and 
disappeared as soon as chemists fell upon accurate methods of 
analyzing common air. 
9. Experiments upon Vegetables, discovering their great Power 
of purifying the Common Air in the’ Sunshine, and of injuring it 
an the Shade and at Night. To which is joined a new Method of 
examining the accurate Degree of Salubrity of the Atmosphere, 
London, 1779.—This is an octavo volume of 302 pages, which Dr. 
Ingenhousz ia ag in 1779, just before setting out for the 
continent. He gives an account in it of a set of experiments 
which had occupied him incessantly for about three months 
during the preceding summer. Only two points are established 
in this book. 1. That the leaves of plants give out oxygen gas 
when exposed to the sun under pump water. 2. That the propor- 
tion of oxygen in the air immediately in contact with plants is 
diminished during the night. But whether this is owing to the 
absorption of oxygen, the emission of carbonic acid, or the 
conversion of the oxygen into carbonic acid, is not ascertained. 
Dr. Ingenhousz, at the time he made his experiments, had no 
accurate ideas respecting the composition of air, nor respecting 
the action of nitrous gas on air. He was not aware of the 
different nature of hydrogen and carburetted hydrogen gas, and 
perpetually confounds. them together. M. Theodore de Saus- 
sure’s experiments on this subject are much more precise ; 
though even he has not thrown so much light upon it as is to be 
wished. Dr. Ingenhousz in this case, as in his explosions with 
common air and ether, had the merit of commencing the inves- 
tigation; but his progress in it was very small. 
The method of determining the goodness of air, described in 
this book of Dr. Ingenhousz, is merely the Abbe Fontana’s, a 
little ‘abridged, and throws no additional light upon the consti- 
tution of air. . 
