No. 1072, Vol. 42] 



NA TURE 



63 



interesting to know how the difficulty has been got over. 

 When the high-pressure piston is at the end of its stroke, 

 the low-pressure piston will be at the middle of its stroke, 

 the cranks being at right angles ; and if by any means 

 steam could be admitted to the low-pressure cylinder 

 without affecting the high-pressure piston, the engine 

 would, of course, be able to turn round half a revolution, 

 and so place the high-pressure piston immediately in a 

 position to commence its stroke. The " intercepting 

 valve," as it is called, is an arrangement by which the 

 passage between the high- and low-pressure cyhnders 

 can be closed, and at the same time admits steam to the 

 low-pressure cylinder when the high-pressure piston is on 

 one or other of its dead points. This arrangement con- 

 sists of a valve in the passage between the cylinders con- 

 nected to a small piston in a cylinder placed in a suit- 

 able position. The steam supply is taken from the main 

 steam-pipe, and regulated in its passage to the small 

 cylinder by a valve worked from the foot-plate. If the 

 engine refuses to start when the regulator is opened, the 

 lever connected to the intercepting valve apparatus is 

 pulled over. This admits steam behind the small piston, 

 which immediately is forced forward and closes the inter- 

 cepting valve, at the same time opening a port through 

 which the steam is admitted to the low-pressure cylinder. 

 This starts the engine, and the lever is returned to the 

 running position by means of a spring. The rise of 

 pressure in the passage between the cylinders, owing to 

 the exhaust from the high-pressure cylinder, opens the 

 intercepting valve, and compound working commences. 

 This arrangement is very simple and trustworthy in 

 practice. A large number of Worsdell compounds are 

 now in use in India and elsewhere with admirable results. 

 Where coal costs forty shillings and more per ton, it is 

 very important that the most economical engine should 

 be used. 



On the Brighton Railway very economical results 

 have long been obtained with the ordinary locomotives 

 designed by the late Mr. Wm. Stroudley, and are due to 

 the general excellence of design of boiler and engine, 

 coupled with careful driving, induced by the coal premium. 

 If locomotives were generally worked more by the re- 

 versing lever and less by the regulator, more economical I 

 results would be recorded ; or, in other words, expansive ' 

 working means economical working, which in the ordin- 

 any engine depends on the driver. In this manner, to ' 

 work steam expansively in the non-compound locomotive, j 

 it is necessary for the driver to regulate the power of the I 

 engine by varying the quantity of steam used in the | 

 cylinders by means of an earlier or later cut-off, regulated 1 

 by means of the reversing gear, the supply from the | 

 boiler not being checked in any way when running. On 

 the other hand, the engine can be regulated by varying 

 the steam supply at the regulator, the degree of expansion 

 in this case being such as the driver chooses to generally 

 use. Under the first conditions all the steam used is : 

 worked expansively, and under the latter the cylinders < 

 are choked with steam at one minute, and have an 

 insufficient supply at the next. On the other hand, 

 with the compound engine the steam must be expanded 

 to a certain extent whether the driver likes it or not, and 

 a result may be obtained with careless driving from the 

 compound which would be passable when shown by a 

 fairly well driven ordinary engine. 



Mr. Drummond, the Locomotive Superintendent of the 

 Caledonian Railway, has been making extensive experi- 

 ments with steam-pressures varying from 150 to 200 lbs. 

 per square inch, with identical engines doing practically 

 the same work, the results of which will be given to the 

 Institution of Civil Engineers. Without dealing with the 

 practical difficulties involved in the use of such high pres- 

 sures in non-compound locomotives, it will be highly 

 interesting to know the results of these experiments. 

 Whether the saving in fuel will equal or exceed the com- 



pound results obtained by Messrs. Webb and Worsdell is 

 a moot point. 



It has been observed that the saving of fuel due to a 

 compound locomotive when working similar trains with 

 the non-compound engine is due to the higher pressure 

 used, and that when the pressure is reduced to the same 

 level as that used in the non-compound engine the saving 

 in fuel at once drops considerably, and the results give a 

 little saving in favour of the compound. From this it is 

 evident that to alter an ordinary engine to the compound 

 system, without raising the working pressure, will be of 

 little good, and not worth the cost. 



The many statements made in order to prove the more 

 economical working of the compound over the non- 

 compound locomotive are misleading in the extreme, and 

 as a fair comparison of the two types they are of no 

 value. The compound locomotives have large boilers, 

 ample heating surface, and all recent improvements, be- 

 sides the all-important feature of a working pressure of 

 175 lbs. per square inch. This engine is compared with 

 an ordinary non-compound locomotive having a smaller 

 boiler, generally hard pressed for steam, because it has to 

 haul its maximum load, with a working pressure of about 

 150 to 160 lbs. to the square inch. To put two such 

 engines into competition is absurd, and therefore the 

 results obtained by the compound locomotives in every- 

 day working cannot fairly be compared with the non- 

 compound engine's records. 



For these and other reasons engineers are anxiously 

 waiting to learn the results of Mr. Drummond's experi- 

 ments, for then for the first time will it be possible to 

 fairly compare the two systems. 



It must not be imagined that because the compound 

 and triple expansion marine engine is so successful in 

 fuel economy, the compound locomotive is also likely to 

 be so : the conditions of working are so totally different ; 

 for instance, the engines of an Atlantic liner work for 

 seven or more days, doing practically the same amount 

 of work the whole time, and since the work is constant 

 the engines are designed to do that work in the most 

 economical manner. With the locomotive, on the other 

 hand, the work is never constant, and for that reason the 

 steam supply is an ever-varying quantity, besides the 

 constant stopping and reversing always going on when 

 any shunting has to be done. These conditions are fatal 

 to very economical working, and more especially when 

 applied to a compound locomotive. 



The compound principle is a sound one, but one not 

 likely to be generally adopted, on account of extra com- 

 plication. The present consumption of fuel by ordinary 

 well-designed non-compound locomotives (take, for in- 

 stance, the Brighton average consumption of 2475 lbs. per 

 mile for all their passenger engines) has not been beaten 

 by the compound locomotive records ; and until it can 

 be demonstrated that a distinct economy is possible by 

 their general use, they are not likely to increase largely 

 in number. N. J. L. 



NEW ZOOLOGICAL PARK AT WASHINGTON. 



BY an Act of Congress passed on March 2 last year, an 

 " appropriation" was made for the establishment of 

 a Zoological Park in the district of Columbia "for the 

 advancement of science and the instruction and recrea- 

 tion of the people." The control of the establishment 

 was intrusted to a Commission composed of the Secretary 

 of the Interior, the President of the Board of Commis- 

 sioners of the District of Columbia, and the Secretary of 

 the Smithsonian Institution. 



Although the Commission was thus established only a 

 year ago, the three Commissioners have already set to 

 work, and, as we learn from their report, transmitted in 

 January last to the Senate and House of Representatives 



