462 



NATURE 



[April II, 1878 



The second division of the book is devoted to the con- 

 sideration of the block system, first conceived by Sir 

 William Fothergill Cooke, and to the instruments and 

 regulations by which that system which is the great 

 guardian of the safety of railway travelling is carried out. 

 It begins with a short historical notice of the subject, and, 

 after explaining some of the elementary principles upon 

 which the various instruments are constructed, proceeds 

 to describe the different systems for carrying the block 

 system into effect. The chapters devoted to this subject 

 are embellished by a large number of excellent illustra- 

 tions ; each system being treated in a chapter to itself, 

 which is a tolerably complete treatise on the subject. 



of sections or " blocks," and the traffic is so regulated, that 

 it is impossible for two trains to be in the same section 

 at the same time. As a train enters one section, the 

 signal behind it is set at danger, and is not lowered until 

 the train has passed into the next section, which is 

 similarly protected, and thus throughout the whole of its 

 course a train cannot follow it at a distance less than the 

 length of a section, or the distance between signal and 

 signal. This is the one principle of the block system 

 and all the various arrangements devised by different 

 inventors differ only in the details by "which it is carried 

 out. 



In Rousseau's arrangement, which may be taken as a 



Fig. I, 



The beautiful arrangements of Mr. Preece, in which 

 the indications of the signalling instruments as well as 

 their manipulation are identical with those of the outdoor 

 signals, are clearly described, as well as the systems of 

 Mr. Walker, of Messrs. Tyer, and of Mr. Spagnoletti, all 

 of which are very extensively used in this country. The 

 system of Messrs. Siemens Brothers so largely employed 

 on the Continent, a description of which concludes this 

 part of the book, is specially remarkable for the fact that 

 in it batteries are dispensed with, the necessary electric 

 currents for working the instruments being derived from 

 small magneto-electric machines. 



^ 



Fig. 2. 



«/• 



c a" 



The various schemes that have been devised for making 

 the train work its own signals, either by depressing 

 " treadles " on the line, or by otherwise making electrical 

 contacts, form a very interesting chapter, in which the 

 systems of Mr. Imray, of London, of Mr. Rousseau, of 

 New York, and of Dr. Whyte, of Elgin, are described 

 and rendered clear by means of drawings and diagrams 

 of the apparatus. 



The essential principle of what is known as the block- 

 system, is the insuring of there always being a certain 

 distance between two trains travelling on the same line of 

 rails. To carry this out the line is divided into a number 



Fig. 3. 



type of the automatic systems of block signalling, the 

 train in its progress depresses treadles on the line, which, 

 by making electrical contacts with suitable apparatus, 

 set the signals at danger as the train enters one section, and 

 releases them as it passes into the next. A general idea of 

 this system maybe obtained by referring to Fig. 2, in which 

 A, B, and c represent three signals, and the spaces A B and 

 B c two sections of the line ; at a is a treadle by which A is 

 set at danger, and at a' is another by which it is released ; 

 similarly a treadle at b sets the signal B at danger, and a 



Fig. 4. 



second at // lowers it to the all clear position." A train, 

 therefore, in passing a, which it does just before entering 

 A B, will block that section against following trains by the 

 signal A ; travelling to B it will, in passing b, set B at 

 danger, and not until it passes a', when it is well out of 

 the section ab, can the signal a be set at all clear, 

 permitting a following train to enter A B. 



In the system of M. Brunius, which is under trial on 

 the state railways of Sweden, telegraphic communication 

 is made between the stations and the engine of the train, 

 so that not only can ordinary signals be transmitted tc 



