102 
NA LORE 
[ DECEMBER 3, 1903 
given type. 
of each class of instrument, but this is of too frag- 
mentary a nature to be of value; we may direct atten- 
tion to the fact that the discussion of hot-wire instru- 
ments is incorrect; no mention is made of the cooling 
of the wire, and it is apparently assumed that the 
instrument is kept in the circuit for exactly one second 
whenever a measurement is made. 
It is a pity, seeing how much trouble has been taken | 
with the drawings of the working parts and the wide 
acquaintance with instruments which is evidenced, 
that Mr. Parr has not given us a more valuable work. 
As it is, the book may prove useful to those who may | 
be called upon at any time to put something right in 
an instrument which has broken down. Mis: 
Life in Mind and Conduct: Studies of Organic in 
Human Nature. By Henry Maudsley, M.D. Pp. 
xv+444. (London: Macmillan and Co., Ltd., 1902.) 
Price tos. 6d, net. 
Reapers of Dr. Maudsley’s former volumes will find 
in the present work both the faults and the merits of 
its predecessors. Dr. Maudsley here, as always, writes 
with a great deal of epigrammatic felicity, and shows 
from time to time vivid flashes of insight into human 
character; here, too, as formerly, he often mars the 
effect of his epigrams by a tendency to re-elaborate 
them into rhetorical ‘‘ common-places,’’ in the technical 
sense of the term. The fundamental positions of the 
book may be reduced to three : the worlds of mind and 
of matter in reality form a single continuous evolu- 
tion; ‘‘ whatever is, is right,’’ being an inevitable 
result of the laws of that evolution; ‘‘ private vices ’’ 
are, as Mandeville taught, ‘‘ public benefits,’’ inas- | 
much as vice and virtue are alike expressions of the 
GG 
_ needs of the “‘ social organism.’’ On this last topic 
Dr. Maudsley writes a great deal that is striking and 
not a little that is true, but he never explains how upon 
his principles the recognition of any distinction 
between right and wrong can be other than an | 
absurdity. If the whole of morality is devotion to the | 
advancement of society, and if, again, the advance- | 
ment of society is equally promoted by virtue and by 
crime (and this is what Dr. Maudsley more than once | 
asserts), why should we make any distinction between | 
the hero and the criminal? That God brings good out 
of evil is a truism; it does not follow that the evil is 
therefore as good as the good. (ARE D. 
Elementary Bacteriology. By M. L. Dhingra, M.D., 
CM" Edin, DD 2PsHL, (Cambs Pp. xiv 145. 
(London: Longmans, Green and Co., 1903.) Price 
gs. neti 
From the preface we learn that this little book has | 
been written especially for Indian students and prac- 
titioners. Too much has been attempted in the space, 
and the descriptions suffer from extreme brevity, only 
the fringe of the various subjects dealt with being 
reached. For example, no less than sixteen disease 
conditions are discussed in about forty pages, ex- 
cluding the space allotted to illustrations, &c. 
information given, so far as it goes, is as a rule 
accurate, the introductory portion upon the morpho- | 
logy and general biology of the bacteria being perhaps 
the most satisfactory. Subjects of especial interest to 
the Indian practitioner, e.g. protective inoculation 
against cholera, receive little more attention than 
many others which only indirectly concern him; 
actinomycosis is allotted more than a page, madura 
§ 
disease less than half a page. In the concluding 
pertions of the book immunity, the principles of 
bacteriological technique, and antivenene are similarly 
dealt with. The book is well and sufficiently illus- 
trated. R. T. Hewtert. 
NO. 1779, VOL. 69] 
There is a general discussion of the theory 
The | 
LEDRERS LO) TEER TIMNO Te 
| [The Editor does not hold himself responsible for opinions 
expressed by his correspondents. Neither can he undertake 
to return, or to correspond with the writers of, rejected 
manuscripts intended for this or any other part of NATURE. 
No notice is taken of anonymous communications.] 
| 
| A Useful Empirical Formula. 
| My note in Nature of October 8 may be extended. I 
found that one of my pupils, Mr. Glasgow, was assuming 
that the expansion and compression parts of a gas engine 
diagram followed laws of the type pv” constant; in cases 
where there was a probability that the clearance had not 
| been measured accurately, so that v being the measured 
volume and c the constant error, he assumed p(v+c)" to be 
constant, and he was enabled to find ¢ from the curve. 
There is no reason to believe that these curves ought to have 
such a law, although, curiously enough, following this 
assumption, the clearance obtained from the compression 
curve is usually not very different from that obtained from 
the expansion curve. Mr. Glasgow’s method of finding c 
is much the same as what I shall now describe. An 
empirical formula of the type 
y=a+bx" 
would be exceedingly useful in many parts of pure and 
applied science if, when given a table of values of y and x, 
we could readily find a, b and n. I have often sought for 
a method of working, but without success. If a is zero, we 
have only to plot log y and log x as the coordinates of 
points on squared paper. If a is not zero, there is a clumsy 
method of using logarithmic paper which may be adopted, 
but it is not satisfactory. We now have a method easy of 
application. Thus values of x and y being given, draw the 
curve AB shown in the figure. Set off any convenient angle 
DOX. Select the point P. Draw PD, XF, FEQ, EH, &c., 
the lines XF, EH, &c., being at 45°. Project horizontally 
from the points POR, &c., to M, U or N, W or V, &c., 
letting lines at 45° from M, U, &c., meet the horizontals 
at N, V, X, &c. If the above law holds, N, V, X, Z lie 
in a straight line. If they lie only approximately in a 
straight line, draw the line N’O! lying most evenly among 
them. Then OO! is the value of a, and n is 
| log (1+tan N/O/Y)/log (1+tan DOX), 
and b is readily~ found. 
I may say that we have no great difficulty in testing 
| whether a curve follows approximately a law like 
y—a=b(x—B)”. 
| For this we have the curve on tracing paper, and we try 
| as in the figure, then slide the curve a short distance in the 
| direction x and try again, and so on. After a little study 
Mr. Glasgow has discovered a number of interesting proper- 
ties of curves of these types. Joun PERRY. | 
