EE VIEWS. 
81 
savant which is nothing "better than a tricky cloak for ignorance. We were 
glad, therefore, in a former number, to perceive a new edition of Dr. Arnott’s 
well-written treatise ; and to the first part, which then came under our notice, 
we awarded such praise as we believed the book to deserve. Part II. has 
now appeared, but we must candidly confess it has not fulfilled our antici- 
pations. It is “ behind the time,” contains no account of the progress of 
physics during the last few years, and is in some cases remarkably inaccurate. 
What shall we say, for example, of a treatise, in which the splendid results 
of Tyndall’s researches are left unnoticed, and in which the principles and 
discovery of the spectroscope — the most wonderful scientific instrument of 
the present century — remain unexplained ? Dr. Arnott’s descriptions are 
clearly written, and in most cases are sound ; but he has not done justice to 
many of the departments of science upon which he has written ; he has 
attempted too much and effected too little. Had he left out much that he has 
said about the knowledge of the ancients, had he tried to be less classically 
erudite and more strictly scientific, he would not have damaged his early repu- 
tation, and would have materially benefited the amateur student. Why does 
he dismiss the principles of the compound microscope in a few paragraphs l 
Why is there no mention of the ophthalmoscope and laryngoscope ? Why 
are all the physical wonders of photography disposed of by saying that 
“ This new art is called photography ” ? Why do we not find a syllable about 
the Casselli or Morse’s telegraph ? These are all questions which the public 
has a right to ask of the author. 
The chapters upon optics are by far the best in the volume, and in dealing 
with some of the complex questions of this branch of natural philosophy, 
Dr. Amott has shown his clear, terse method of explaining difficult problems. 
A subject which more than any other has puzzled physiologists is the fact 
that we perceive objects in their true position, although on the retina of the 
eye they are depicted inverted, as they are in a camera obscura. This fact 
leads our author to the following remarks : — 
“ The explanation is simple. It is known that a man in bed, with his, 
cheek on the pillow, judges as correctly of the position of the objects around 
him as any other person, never deeming them to be inclined or crooked 
because their images on his retina are inclined, in relation to the natural 
perpendicular when the head is erect. And boys who at play bend themselves 
downwards, to look backwards from between their knees, although a little puz- 
zled at first because the usual position of the objects on the retina are reversed, 
soon see as correctly in that way as in any other. It appears, therefore, that 
while the mind studies the form, colour, etc., of external objects in their 
images as depicted on the retina, it judges of their position, not by the acci- 
dental position of the images on the retina, but by the direction, as ascertained 
by the touch and experience, in which the light comes from the object and 
its parts towards the eye — no more deeming an object to be placed low because 
its image is low in the eye, than a man in a room into which a sunbeam enters 
by a hole in the window-shutter deems the sun low because its image is on 
the floor.” 
VCL. V. — NO. XVII T. 
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