NATURE 
[ApRIL 15, 1897 
coefficient is a result of something between the two, 
perhaps rather nearer to Dr. Siemens’ theory. 
Mr. Wilkinson does not seem to be very clear as re- 
gards the waters in which teredoes may be expected. 
This is a question of temperature rather than of depth. 
Brass taping was first applied for this purpose to the 
core of some of the “ Eastern Extension” Company’s 
cables in 1879 by the Telegraph Construction Company ; 
but it should be understood that this is only used for 
those types deposited in waters above a certain tempera- 
ture. By bringing home picked-up cables, however, and 
laying them afterwards in another part of the world, 
the germs of the teredo and other boring nuisances 
sometimes present themselves in places where they had 
not previously appeared. 
Mr. Wilkinson is evidently of opinion that you should 
find your cable before you make it, for he starts off with 
a goodly selection of the implements of war as regards 
the various forms of grapnels employed. To these he 
should add that of Mr. Henry Benest. As a cutting and 
holding grapnel, it has done admirable service. 
Let us now turn to the electrician’s side of the question. 
The electrical portion of the book is very complete as 
regards testing, and especially in methods of fault 
localisation ; but it might be more so with reference to 
the apparatus. The new universal galvanometer of Mr. 
H. W. Sullivan, on the suspended coil principle, is well 
illustrated, but not quite correctly described. In the first 
place, unlike the Thomson marine galvanometer, there 
is no ironclad cover. Messrs. Weatherall and Clark’s 
ingenious damping device for the “ Marine” instrument is 
dealt with, showing how sensitiveness may be maintained 
though a suspension is made dead-beat. The principle 
and working of Varley slides are beautifully illustrated 
on p. 267, after the manner shown by Mr. W_ A. Price.t 
Testing keys are dwelt on ad znfinttum. With regard 
to the battery employed, surely Leclanché cells of any 
size. with an internal resistance of as much as 5 ohms, are 
unusual, if the cells are in good condition. Why does Mr. 
Wilkinson introduce the legal volt here? Surely in this 
class of work the old B.A. unit may be adhered to? For 
testing batteries, the author should remember that it is only 
Muirhead’s method (and the modifications of Kempe and 
Munro) which are free from the objection of running 
down the battery during the test in such a way as to vary 
the E.M.F., and so give false impressions. Mr. Wilkinson 
describes a test of his own, on p. 223, for simultaneously 
testing the resistance and electro-motive force of a battery, 
which certainly looks hopeful. 
In speaking of thirty seconds as a time allowance for 
making a “bridge test” during repairing work, it must be 
remembered that on anything like a long length of cable 
(and especially if partially coiled up), it takes a material 
time for the line to acquire its true potential throughout. 
This book gives a certain amount of information regard- 
ing the physical and electrical effect of temperature and 
pressure on gutta-percha, besides references to the present 
writer’s contributions on the subject by way of explana- 
tion. It should be remembered, however, that, in selecting 
a type of core, the proportions are almost entirely governed 
1“ A Treatise on the Measurement of Electrical Resistance,” by W. A. 
Price. (Clarendon Press, Oxford.) 
NO: 1433, VOL. 55] 
by economical considerations for a given “ K R” to effect 
a certain working speed with a limiting factor of safety 
from a mechanical standpoint. 
With regard to the localisation of faults, Mr. Wilkinson 
gives us admirable accounts of the more recent methods 
of Sir Henry Mance, C.1.E., Mr. A. E. Kennelly, and 
others ; besides the fall of potential test, due to Mr. 
Latimer Clark, with the special modification (for ship 
to shore work) of Mr. J. Rymer-Jones. The author 
does not, however, appear to show that in fault-testing a 
great number of observations should be made, besides 
various methods adopted for checking purposes ; neither 
does he point out that no values should be used in 
after-calculations which appear, by comparison with the 
rest, to be untrustworthy. It is also advisable to 
discard results from one test which appear valueless 
by comparison with those obtained from the other 
methods adopted. No hard and fast rules can be 
made for fault-testing; much must be left to the 
individual judgment of the electrician according to 
prevailing conditions, character of fault, &c. Though 
a fault may have a low resistance, it is sometimes 
as variable as a high resistance fault ; and, if so, it gives 
equal trouble to locate. One great point to be aimed at 
is, of course, to make the observations at the moment 
when the fault is least variable. With reference to 
Kennelly’s break test, experience seems to show that the 
distance of the break from the testing station, in no way 
detracts from the value or efficiency of the test—not- 
withstanding Mr. Wilkinson’s remarks. For other ways, 
however, it is well if the fault be fairly near. If the 
resistance up to the fault be great, then the battery power 
should be made in proportion, according to Ohm’s law 
for a given required current. Mr. Wilkinson’s limitation 
to the voltage employed in this test would, under certain 
conditions, be liable to materially reduce the value of the 
test from a point of accuracy. In a future edition the 
author should describe the reproduction method of taking 
Kennelly’s test. It is in several ways preferable to work- 
ing with the bridge, especially with a variable fault, as 
observations are made much quicker. Again, it involves 
the use of only one (dead-beat) galvanometer, thereby 
simplifying the carrying out of the test, besides reducing 
the chances of error. With Sullivan’s galvanometer, this 
method, even on board ship, is found to give excellent 
results. Elsewhere in the book the author well describes 
and illustrates Mr. Willoughby Smith’s ship and shore 
test during laying operations, besides the modification 
of the above, for fault-testing, as devised by Mr. H. A. 
Taylor. ; 
The author also deals cursorily with land lines, de- 
scribing the underground and beach systems of the 
Eastern Telegraph Company (as devised by Messrs. 
Clark, Forde, and Taylor), besides those of the present 
writer. Moreover, in this connection the Saunders and 
Bright Lightning Guards are respectively described. 
Finally, so far as it goes, Mr. Wilkinson and the 
Electrician Printing and Publishing Company are to be 
congratulated on the above book as a treatise contain- 
ing a vast amount of practical information in com- 
paratively few words, such as are well adapted for study 
by the submarine telegraph engineer and electrician. 
The illustrations are admirable and almost entirely 
