April II, 1878] 



NATURE 



463 



the engine-driver, but he can receive instructions by 

 telegraph. 



Miscellaneous appliances employed in railway tele- 

 graphy are treated in the third division of Mr. Langdon's 

 book, and an interesting chapter is devoted to the various 

 " signal repeaters " and " light recorders.'' By the former, 

 which were first employed by Mr. Preece, the position of 

 the out-door signals is reproduced in miniature within 

 the signal box, so that the signalman knows at once if 

 the outside signals are correct. Light recorders are 

 instruments which give warning, within the signal box, of 

 the extinction of the light of the outside night-signals. 

 Of these several forms have been devised but they all 

 depend upon the expansion of metallic substances when 

 subjected to the influence of heat and their subsequent 

 contraction when that heat is removed. Fig. 3 is a cross- 

 section of the transmitting portion of one of these instru- 

 ments, in which B represents a concave disc of copper 

 attached by its edge to the ring A A, a short distance above 

 the flame of the lamp. When the light is out the lever D 

 rests on the contact screw attached to the arm F (as 

 shown in the figure) and the circuit is closed between 

 the "line" and the earth, and an electric bell is set 

 ringing in the signal box at the same time as an instru- 

 ment indicates the words " Light outr When, however, 



Fig. s. 



the plate B is heated by the flame below it, it becomes 

 expanded, lifting the stud c, which, pressing against the 

 lever D, lifts it off the contact screw, thereby breaking the 

 circuit. The bell ceases ringing and the indicating instru- 

 ment falls back to the signal " Light /«." 



Figs. 4 and 5 represent a different arrangement for pro- 

 ducing the same result, in which the contact-maker con- 

 sists of two compact barsof dissimilar metals, constructed 

 afcer the manner of a metallic pyrometer, and united 

 together at the end A with the similar metals facing one 

 another. By this arrangement the arc of motion is largely 

 increased and the instrument is in consequence rendered 

 more sensitive. Under the influence of heat the bars 

 curve in opposite directions, as shown in Fig. 5, but on 

 the light becoming extinguished their differential contrac- 

 tion brings them to the position shown in Fig, 4, contact 

 is established, the bell rings, and the signal " Light ^«/," 

 is transmitted to the receiving station. 



The important subjects of the interlocking of points and 

 signal levers, of level crossings, and the working of rail- 

 way yards, all find their place in Mr. Langdon's book ; 

 and very interesting chapters are devoted respectively to 

 the various kinds of electric bells, to lightning protectors 

 for telegraphic instruments, and_ for the methods devised 



by diff'erent inventors and adopted by different railway 

 companies for establishing intercommunication in trains. 



It is not easy within the limits of the space at our dis- 

 posal to do anything like justice to Mr. Langdon's most 

 useful work, which is a thorough exposition of the subject 

 in all its branches by one who not only has had a very 

 large practical experience of the application of electricity 

 to railway working, but who has the gift of clear descrip- 

 tion and a power of interesting his readers. 



To all engaged in railway management whether 

 directors, engineers, traffic managers, station-masters, 

 signal-men, engine-drivers, or guards, Mr. Langdon's 

 work will become a necessary text-book and book of 

 reference, and the general scientific reader will find it 

 most interesting and instructive. We must congratulate 

 its author upon having put so much valuable information 

 in so small a space, and its publishers upon having issued 

 it in so cheap and attractive a form. C. W C. 



TROLLOPE'S ''SOUTH AFRICA " 

 South Africa. By Anthony TroUope. (London : Chap- 

 man and Hall.) 

 THERE are probably few of our Colonies the rela- 

 tions of which to one another are so little understood 

 by the general public as those of South Africa, and none 

 where events of so extraordinary a nature have occurred 

 within the last few years. There are few Englishmen, 

 therefore, by whom these charming volumes will not be 

 read with delight and interest, coming as they do from a 

 man of so much experience and of such liberal views as 

 Mr. TroUope. The arrangement of the book is good and 

 clear, each of the colonies being treated separately ; a 

 few chapters being devoted to a general introduction, 

 and a few to the native tribes. The author has been led 

 thereby into a somewhat unnecessary, possibly uncon- 

 scious, repetition, when introducing each new district to 

 his readers. This clearly arises from the fact that the 

 origin of each colony is the same— the desire of the Boers 

 to free themselves from British rule, their consequent 

 occupation of new lands beyond the English border, and 

 the necessity of our ultimately stepping in to govern them, 

 both for their own good and for that of the natives. Mr. 

 TroUope states that the objects of his interest are men 

 and women, and it is to learn their condition, both 

 socially and politically, that he visited South Africa. 



Cape Colony, the oldest, largest, and most flourishing 

 one, contains at present about 750,000 inhabitants, one 

 third only of whom are white, and of the latter but one- 

 third are English. These numbers indicate at once the 

 very slow progress of the colony, and show that it 

 is far from popular amongst emigrants, which Mr. 

 TroUope thinks is due to the fact that here, and here 

 only, the white labourer has to compete on equal terms 

 with the native. The country seems closely to resemble 

 the Riviera, though on a larger scale, both in scenery 

 and capabilities. A great deal of the best lands, about 

 80,000,000 acres, is in private hands, of which only 

 550,000 acres are cultivated, being i- 145th of the private 

 lands, and not one-fourteenth as Mr. TroUope has it. 

 The great drawback to the country is the want of irriga- 

 tion works when almost every European plant could be 

 grown. Amongst other things, has not the cultivation of 



