192 



NATURE 



\yan. 2, 1879 



ness was really in dispute, and how much Peach's obser- 

 vations went to settle it. No one reading the volume, with 

 its account of Dick's hammerings and Hugh Miller's 

 visits and writings, could surmise that in the palceontology 

 of the Old Red Sandstone of Caithness Peach has done 

 far more than Dick, far more than Hugh Miller, more, 

 indeed, than all other geologists put together. 



The illustrations of Caithness scenery, plentifully in- 

 terspersed throughout the book, are well engraved, and, 

 on the whole, very faithful and characteristic. Nothing 

 could be better than the Deil's Brig of Scrabster Bay. 

 We see the very lichens quivering in the gusts that blow 

 for ever through that hideous cleft, and we hear the 

 screams of the northern sea-fowl as they wheel in rest- 

 less circles from the neighbouring Clett. In transferring 

 the author's sketches to the wood, however, the artists 

 have taken a few liberties which would have roused poor 

 Dick's indignation. Dirlet Castle, which stands on a 

 rock some twenty or thirty feet above the stream, is 

 raised at least 300 feet into the air ; and dear old Morven, 

 glorified into a second Matterhom, is placed just opposite 

 to Dick's contemptuous ridicule of what the books say 

 about the hill — " None of the hills are as big as books 

 make them" — "downright nonsense ! Morven is acces- 

 sible on every side." Arch. Geikie 



TELEGRAPHY 



Ittstruciioiis for Testing Telegraph Lines and the Tech- 

 nical Arrangements of Offices. By Louis Schwendler. 

 (London : Triibner and Co., 1878.) 



THE criterion of the good working of a line of telegraph 

 is its freedom from interruption. Interruptions to 

 the communication are technically called " faults," and on 

 our overground lines men are stationed at certain intervals 

 for the express purpose of patrolling these lines and 

 removing defects from them that sooner or later might 

 culminate in faults. Of course accidents, such as those 

 arising from snowstorms and violent winds, cannot be 

 prevented, but most of the interruptions that are met with 

 in practice can by proper supervision be eliminated before 

 they can arrive at such a condition as to interfere with 

 the communication. In telegraphy more than in any- 

 thing else, " prevention is better than cure," and for 

 many years past all our telegraph engineers who have 

 devoted their attention to the proper maintenance of tele- 

 graphs have striven to devise as perfect a method as they 

 can for detecting the presence of faults and for establish- 

 ing an accurate system of testing. 



It is, however, upon our submarine cables, not only in 

 their manufacture but during the process of laying, and 

 whilst subsequently working, that the greatest skill and 

 ingenuity has been employed to devise a perfect system 

 of testing. 



The fii"st rational mode of testing our cables was intro- 

 duced by Dr. Siemens, but Mr. Varley had previously 

 introduced into the service of a Telegraph Company a very 

 elaborate system of testing by the aid of differential gal- 

 vanometers and resistance coils. Rheostats or resistance 

 coils had been invented by Wheatstone as far back as 

 1843, and Sir Charles Bright and his brother, Mr. Edward 

 Bright, had introduced them into use on the Magnetic 

 Telegraph Company's system. It was, however, in the 



telegraph companies' service that the system was to a 

 certain extent perfected, and when all the systems of the 

 different companies were concentrated into the hands of 

 the General Post Office the system became universal for 

 the whole country. We cannot think that Mr. Schwendler, 

 when he asserts that no really practical system of testing 

 had been adopted by any other telegraphic administration 

 than that of India, could have been aware of the perfect 

 system in use by our English administration, and it is a 

 pity that he has not embodied in his book a description 

 of the system in use in England. This perhaps is un- 

 necessary, because it is fully detailed in the " Handbook 

 of Practical Telegraphy," by Mr. CuUey, and in the text- 

 book of science on " Telegraphy," by Messrs. Preece and 

 Sivewright. Moreover, there is an excellent little " Hand- 

 book of Testing" detailing not only the practice on land 

 lines but on cables also, by Mr. H. R. Kempe, and with 

 another capital little book by Capt. Hoskiaer, on ''testing 

 cables," as well as a work on " Electrical Measurements," 

 by Mr. Latimer Clark, leaves very little to be desired on 

 the literature of the subject. Mr. Schwendler really adds 

 little or nothing to our knowledge of the subject, and his 

 book is only valuable as an indication of what has been 

 done in India. 



Great strides have been made in the Telegraphic De- 

 partment in India ever since the accession to power of 

 the lamented Col. Robinson. There is, according to Mr. 

 Schwendler, a large staff of officers available with a first- 

 rate general education and with a strong desire for 

 improvement, and many of them are well trained in con- 

 ducting physical experiments. It is to be hoped that 

 their education is sufficiently advanced to enable them to 

 follow the rather intricate mathematical developments of 

 ]Mr. Schwendler. If his book has a defect it is that it is 

 overloaded with mathematical investigations. There is 

 no necessity to appeal to laboured formulae when simple 

 observations alone are needed to interpret pheno- 

 mena. The mathematician loves his formulae as a 

 hen her brood, but the practical man prefers to kick 

 them aside when he can do so and when he can 

 do without them. Now, at p. 16, Mr. Schwendler 

 gives no less than six elaborate formulse, one of which 

 must be selected for each particular condition to enable 

 the tester to discover the value of any foreign electro- 

 motive force that may be in the circuit, the result of what 

 he calls a " natural" current. Now there is no necessit} 

 whatever for any formula. The elimination of earth 

 currents in cable and land testing is of daily and constant 

 occurrence, and it is only necessary to compare the 

 deflection upon any galvanometer given by the eartli 

 current with a deflection produced by one cell through 

 similar resistance to find its value. Readings by reversals 

 when taken rapidly always give a mean that is approxi- 

 mately true, for an earth current rarely varies so rapidl}- 

 as to introduce any sensible error. His formulae for 

 eliminating the electromotive force when measuring with 

 a differential galvanometer simply appal one. 



Mr. Schwendler wisely says, "however much testing 

 may become routine by continual practice it will always 

 and should always partake of something of the nature of 

 a physical experiment which must be conducted with a 

 perfectly clear understanding. Then only can the tester 

 draw the right conclusions from his observed facts ; then 



