30 
THE PHARMACEUTICAL JOURNAL. 
[July 9, 1S70. 
X) 
A 
C B 
Trays be in the same plane; that is, if three rods 
attached to a board in the position of the lines in the 
figure, were used as a model, and the eye of the ex¬ 
perimenter looked in the direction of the arrow, he 
would see the three coincident and appear as one. 
In an experiment with a mirror he 
would see from this point a spot of 
light on looking down R, and in the 
direction of the arrow, he would see 
the hole in the lamp-shade. It will, 
of course, be understood, that the 
number of rays proceeding from the lamp are infi¬ 
nitely numerous. In a diagram, the course taken 
by one only of them can be shown with distinctness. 
But all of those which fall upon the mir ror are re¬ 
flected from tlieir various points of incidence, accord¬ 
ing to the same law. 
5. In the preceding experiment the spot of light 
would appear to proceed from behind the mirror. 
This is also the case with images of persons or 
things seen in ordinary looking-glasses. As a gene¬ 
ral rule, an object appears to be in the direction 
from which the rays which meet the eye last pro¬ 
ceeded. 
The experiment described makes use of a ray 
proceeding from a luminous point. The image of an 
object is the result of the association together of an 
infinite multitude of such points. 
Suppose A B the surface of a mirror. The lines 
I and I 2 represent the paths of rays falling Bom the 
extremities of the arrow upon the reflecting surface. 
Between them there should be an infinite number of 
similar rays proceeding from the intermediate points. 
R and R 2 are the paths of the two rays represented 
after reflection. The arrow, therefore, seems to be 
in the position shown by the dotted lines, which are 
a continuation of R and B 2 , and it appears to be at 
the same distance behind the reflecting surface that 
it is in reality in front. 
In tliis diagram, again, it has been possible to re¬ 
present only those rays which, after reflection, meet 
the eye. From every point of the object, however, 
it will be understood that rays proceed in every di¬ 
rection ; those which are thrown downwards fall on 
the mirror and are reflected, and of these only a 
certain number, viz. those whose paths of reflection 
lie between R and R 2 , are received in the eye. 
6 ; Ordinary objects are visible from almost any 
position the experimenter may take up ; the reason 
is, that the rays of light thrown off from objects in 
general are distributed in an infinite number of di¬ 
rections, owing to the irregularity of their surfaces. 
A beam of light entering through the shutter of a 
darkened room, and falling upon a sheet of paper, 
will do more to illuminate the room than if it fell 
upon a mirror. In the latter case, the light will be 
reflected in one beam, and will afford only one 
bright spot, instead of being distributed in all direc¬ 
tions. 
Manual of Qualitative Analysis. By Robeet Gal¬ 
loway, F.C.S., Professor of Applied Chemistry in the 
Royal College of Science for Ireland. Churchill and 
Sons. 1870. Fifth Edition. 
The title page of the volume before us informs us that 
we are presented with a fifth edition. This fact implies 
one or both of two things : either there is an extraordi¬ 
nary demand for treatises on qualitative analysis, or Pro¬ 
fessor Galloway’s book is better done than others of its 
class. 
Whilst we most willingly accord to the author of this 
work the large measure of praise which he undoubtedly 
deserves, we cannot withhold, at the same time, our opi¬ 
nion, that there is yet room for a good manual of quali¬ 
tative analysis; we might say for two good manuals, for 
we should like to see every one of those already existing 
submitted to a process of sifting. For beginners we 
ought to have displayed all the most important prin¬ 
ciples deduced from just so many familiar facts as would 
serve to establish them in the mind of an intelligent 
school-boy or girl; they would then be in a position 
fairly to attack the subject as it is presented to them in 
the ordinary handbooks. When a child is first regularly 
instructed in writing or drawing he goes through a 
course of “pothooks and hangers,” which, if they have 
no substantive value of their own, familiarize him with 
the nature of the work he has before him, and the tools 
he has to use; but in science, as generally taught, the 
unlucky juvenile is plunged, heels over head, into the 
waters of technicality, the shallows or the deeps of which 
he will be equally lucky if he escape. As an experiment, 
we should like to see some one subject, say botany, taught 
by the guidance of a gradational series of lesson books, 
similar in general principle to ordinary school “copy¬ 
books.” 
Professor Galloway has already made an attempt at 
something of this kind in his ‘ First Step ’ and ‘ Second 
Step ’ in chemistry, but we wish we could think he had 
done so with absolute success. His ‘ Qualitative Analy¬ 
sis,’ which we have just most carefully examined, has 
given us the impression, however, that he has consider¬ 
ably improved with his experience in writing, and par¬ 
ticularly in arranging. If he would now let.the present 
volume stand as a second step, and would take the trouble 
to compile another about one-third of the size, and, not 
disdaining small matters, make it really suited to be¬ 
ginners, he would deserve the thanks of all chemical 
teachers. 
Chemical analysis is an art; its success depends, in 
greatest measure, upon the judicious selection of the de¬ 
vices by which the characteristic properties of bodies are 
brought most prominently into view. One defect of the 
work before us is, that it fails to stamp with sufficient 
distinctness the diagnostic marks of each radicle and 
group of radicles. Unimportant properties and reac¬ 
tions are made as much of, except in the tables, as the 
most distinctive, and consequently the student finds 
none of those salient points to grasp at which ought to 
be ready to his hand. We feel bound to say, however, 
that there is evidence of very careful work. There are 
throughout, so far as we have been enabled to detect, no 
statements which are fundamentally incorrect. 
We like the tables for contrasting the characters of 
the members of the several groups of basylous radicles, 
though we demur to the author’s appropriation of all 
the credit due to the plan, for we find the same thing in 
a slightly different form in many other books. 
