918 
ficult to make them comprehend the na- 
ture of the curvilinear motion. 
The author of this very valuable work 
has done, however, as much as‘could be 
expected from any one, for the general 
reader. He goes through every branch 
of natural philosophy, whether it can 
be referred or not to mixed mathematics, 
and in both partsshews himself eminently 
qualified for the work which he has un. 
dertuken. If in his text he consults the 
ease of the general reader, he gives in- 
formation sufficient in his notes to exer- 
cise the talents of, at times, even the 
higher class of mathematicians. 
The first volume is assigned to me- 
chanicks; the second to hydrostatics, 
pneumatics, and the general principles 
of chemistry ; the third to caloric, op- 
tics, electricity, and magnetism ; the 
fourth to astronomy, aerostation, me- 
teors, weights and measures. ‘This ar- 
rangement doed not appear to us to have 
any advantage over the common mode 
in which the phenomena to be explained 
on mathematical principles are kept by 
themselves, under the heads of mecha- 
nics, hydrostatics, opticss and astro- 
nomy. 
. The first volume begins with a gene- 
ral description of natural philosophy, 
and points out the true rules of philoso- 
phising, not omitting to hold out a ne- 
cessary degree of scepticism, at the same 
time that the student is put on his guard 
“ not to become a blind believer ora 
Useless sceptick.” ‘The general proper- 
ties of matter are then explained, with 
the nature of the laws of motion; and we 
were rather surprised at finding ourselves 
precipitated in the next chapter into the 
difficulties of centripetal and centrifugal 
forces, and the centre of gravity, which 
generally remain till the student has fa. 
miliarised himself with the more simple 
effects of mechanical motion. ‘he the- 
ory of percutient motion then follows, 
and we are brought next to the nature 
of compound curvilinear motion ; in the 
jatter of which the fourth proposition of 
the second section of Newton 1s explain- 
ed. These, to us appearing very dificult 
chapters, are followed by the doctrine of 
motions on inclined planes and of pendu- 
lums ; and then we are introduced to the 
mechanical powers, which in most books 
of this kind are the first things taught, 
and the deviation from the general me- 
thod does not appear to be tollowed by 
any advantage to either teacher or learn- 
er. The chapter on compound engines 
EXPERIMENTAL PHILOSOPHY. 
and machines deserves commendation, 
both in itself and as pointing out fit ob- 
jects for study; for many persons who 
pursue in theory the doctrine of motion, 
tind themselves much at a loss when they 
are called upon to apply their knowledge 
to any. practical purpose. 
The very excellent work of Cotes on 
hydrostatics leaves little to be said on 
the theory ; but many improvements 
have been mude since his timé, particu- 
larly in discovering the specific gravi- 
ties of bodies, and the motion and pro- 
perties of air, which are in this work di- 
lated upon with great propriety. In 
treating the doctrine of optics, we were 
agreeably surprised at finding inserted 
the observations of, as he is called, a 
recent anonymous writer, concerning the 
inflections of light. "They were publish- 
ed in the year 1799, and proceed, we 
understand, from the pen of a gentleman 
who studied the Newtonian theory with — 
great diligence at Cambridge, and after 
an absence of several years returned 
about that time to this country. ‘The 
observations have not been noticed so 
mutch as they deserved ; the experiments 
are ina high degree ingenious, and the 
result is far from establishing the New- 
tonian theory. The author of the work 
before us makes the following remark 
upon the whole of this intricate subject, 
«* A close examination and application of 
this doctrine to a variety of phenomena, 
which have been observed by various inge- 
nious persons, especially of the present age, 
render this theory of colours doubtful in al- 
most all its parts. In the first place, it may 
be doubted whether there really are only 
seven distinct primitive colours, or an indefi- 
nite number of them, which are perhaps pro- . 
duced by some unknown modifications of 
white light. he breadths and the grada- 
tions ot the supposed seven primitive colours, 
in the prismatic spectrum, are the greatest 
foundation for the above-mentioned doubt. 
With respect to the thin transparent plates of 
which all bodies are supposed to consist, we 
are greatly in want of experimental conftir- 
mation; and even if we were sure of their 
existence, it would be difhieult thereby to ex- 
plain, how are the fixed and unchangeable 
colours produced by them in all directions.— 
Such doubts may be seen in all the modern 
writers, On optics, to whose works, which 
are principally t6 be found in Transactions 
of Societies, Toautalep dec: I shall refer the 
inquisitive reader, whd may wish to -be in- 
formed om the subject, or to extend our 
knowledge of nature.” 
The passage of light throngh glasses, 
or reflected by mirrors, may fill volumes, 
