1819.] Scientific Writings of Dr. Ingenhousz. 85 
oxygen gas ; and that only a small proportion of vapour must be 
employed for tle purpose. If we use too much, no explosion 
takes place at all. The combustion-of ether has been investi- 
gated by more modern chemists with considerable precision. 
Mr. Cruikshanks made some progress in the investigation ; Mr. 
Dalton went further ; and M. Theodore de Saussure has obtained 
results which approach to accuracy ; so that but little remains 
in order to complete this important subject. Dr. Ingenhousz 
must be admitted to have begun the investigation, though he 
advanced no further than merely the discovery of the detonating 
power of vapour of ether when mixed with oxygen gas. 
But this paper contains some historical facts which I consider 
as rather interesting. They seem to have been in general over- 
looked by chemists. The person who discovered the fact that 
oxygen and hydrogen gases may be exploded by means of an 
electric spark was Sir William Watson ; undoubtedly, one of 
the most distinguished electricians which England at that time, - 
so rich in first rate proficients in that science, possessed. This 
discovery, trifling as it may appear, deserves to be remembered ; 
because it has contributed so essentially to the progress of an 
accurate mode of examining gaseous bodies. 
The first persons who collected olefiant gas were Messrs. 
f®nee and Cuthbertson. This they did at least as early as 1777, 
by heating a mixture of equal quantities of sulphuric acid and 
alcohol. Mr. Ainew ascertained the specific gravity of this gas, 
its combustibility, and the colour of the flame. It’ was known, 
therefore, though it had not been very accurately examined 
_ before the experiments of the Dutch chemists in 1794. 
Dr. Ingenhousz was of opinion that when gunpowder was 
heated, the nitric acid of the saltpetre gave out oxygen gas, 
while the charcoal gave out inflammable gas, and that the 
explosion was owing to the instantaneous combustion of this 
mixture. It would be needless to make any observations on 
this theory, as it is now known to. be inaccurate in evely 
particular. 
6. On some new Methods of suspending Magnetic Needles. 
Phil. Trans. 1779, p- 537.—Dr. Ingenhousz balanced the needles 
so that they were under the surface of water, and conceived 
that by this method he succeeded in obviating most of the irre- 
gularities in the motions of needles. It is obvious that such a 
method is quite inapplicable to the use of the needle on ship- 
board, which is the great purpose for which it is applied. Nor 
is it at all likely that plunging a needle under water would make 
it answer better for ee iaactiical purposes. 
7. Improvements in Electricity. Phil. Trans. 1779, p. 659.— 
This paper was the subject of the Bakerian lecture for 1779. It 
consists in a historical detail of the progress which the plate 
glass electrical machines had made. Dr. Ingenhousz informs 
us that he had suggested this kind of nfachine about 15 years 
