19*8.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



a05 



much greater uniform velocity than 53 miles per hour, even under very 

 xmfavourahle circumstances, can he obtained down 1 in 100, by gravity ; and 

 that ciinsequently the foundation on which many railway engineers have 

 rested the very pillar of their theory of high rates of resistance at high velo- 

 cities, is utterly without substantiality, — that, indeed, it is a mere fallacy, 

 which will hereafter be numbered amongst the delusions and visions of 

 practical men. 



The whole of the following experiments were made with ordinary working 

 trains, and the object was not to collect minute data from which any 

 scientific results might be deduced, but simply to prove — exclusive of the 

 results of experiments made by either broad or narrow gauge engineers — 

 that what has long been considered an •' established fact" in reference 

 to the resistance to railway trains descending inclined planes by force of 

 gravity, is a mere " circumstance," which, although applicable to narrow- 

 gauge'trains, is utterly inapplicable to hroad.gau.-e trains. The diversities 

 in the rates of speed shown in the workings given below arose, no 

 doubt, from a great variety of causes. Nearly the whole of the portions 

 of the line over which the experiments were made consists of a series 

 of curves, and of cuttings and embankments. The carriages were of 

 different weights, and may occasionally have been well or badly coupled. 

 One day the weather was calm, the next it was unsettled ; in some of the 

 experiments there was a sHglit head wind, in others a moderate side wind 

 from tlie right, or a moderate side wind from the left prevailed, and during 

 tliree of the experiments there was a brisk side wind. Tlie speed, too, at 

 which the trains were running when the steam was shut off would, in rela- 

 tinn to the weights of tlie carriages, as well as to the direction of the wind, 

 enter into the causes of these diversities of speed. We shall, however, not 

 hazard a single opinion on these matters, but confine ourselves to demon- 

 strations that the "formula" of high resistances at high velocities is worth- 

 less in respect of the resistance sdue to broad-gauge trains descending inclined 

 planes by their own gravity. 



In the experiments made down the Wootton Bassett incline with the 

 dynamometer carriage, constructed under the directions of Mr. Brunei, the 

 carriages were weighed to 10 tons each. In no one of the experiments given 

 below, which were made with the ordinary passenger trains, did any of the 

 carriages amount to this weight — that is, they were not full of passengers. 

 The engines employed belong to an old class, and weigh, road-worthy, about 

 23 or 24 tons. 



It has been objected against the experiments made down the Wootton 

 Baisett incline with the dynamometer carriage, that the distance over which a 

 uniform or increasing velocity was attained, viz., 10 or ll-16ths of a mile, is 

 too short to produce a useful practical result. To meet this objection we 

 took the rates of speed not only down the mile and one-eighth of the fall of 

 1 in 100, but down the next seven-eighths* of a mile, which are on a fall of 

 1 in C60 only. The fall of 1 in 100 commences a few chains beyond the 

 85th mile-post, and terminates a few furlongsf beyond the 86|th mile-post. 

 Thence to the 86f th mile-post, the fall is 1 in 660. 



The first experiment was made with a train consisting of four passenger- 

 carriages, three horse-boxes, and one luggage van, weighing about 60 tons. 

 The engine was the " Orion." The table gives the working for the quarter 

 mile immediately preceding the 85th mile-post, as well as from the 85th to 

 the SGJth mile-post. The rails were dry, and very little wind was stirring. 



It will be seen that the speed for upwards of half-a-mile down 1 in 660 is 

 very little below the uniform velocity down nearly three-quarters of a mile 

 of 1 in 100. We merely record the fact, leaving those who have more time 

 at their command than we have ourselves to explain or suggest the causes. 



The second trip was with a train of four passenger-carriages and a horse- 

 box, weighing about 41 or 42 tons, and was attached to the " Mars" engine 

 — rails dry and weather calm. 



The //i/rd trip was with the same engine, with three passenger-carriages, 

 one luggage-van, and two horse-boxes, weighing about 45 or 46 tons. 



The fourth experiment was made with the " Firebrand" engine. The 

 train consisted of three passenger-carriages and a luggage-van, weighing 

 about 36 tons. The carriages were well filled with passengers. 



The//tt experiment was with the " Orion," with four passenger-carriages, 

 three horse-boxes, and a luggage-van, weighing about 59 or 60 tons. The 

 steam was not shut off in this case until the engine- was within a few chains 

 of the 85Jth mile-post. 



The sixth experiment was with the " Load Star." The train consisted of 

 four passenger-carriages and a luggage-van, weighing about 41 or 42 tons. 

 A brisk side wind was blowing. It will be observed that the rates of speed 

 alternate over the whole extent of the 2J miles. 



The seventh trip was with the " Arab," with a train consisting of three 

 passenger-carriages and a luggage- van, weight about 38 or 40 tons — carriages 

 well filled. In this trip we obtained the greatest uniform velocity — rails 

 dry ; weather calm. 



The eighth experiment was with the " Bellona," with four passenger- 

 carriages and a luggage-van, weighing about 41 or 42 tons. 



A brisk side wind prevailed on this occasion, and the same result was 

 produced as in the previous experiment, where a side wind atfected the 

 train, viz., alternating rates of speed. 



The nijith experiment was with tl 'irebrand," with a train of four 

 carriages and a luggage-van, weighi ., ut 45 or 46 tons — rails dry ; slight 

 side wind. 



The ("erart experiment was upon the Bristol and Exeter line from the 174lh 

 to the 176jth mile-post. This portion of the line is on a fall of 45-75 feet 

 per mile, or about 1 in 120. The engine employed was the "Load Star," 

 and the train consisted of four passenger-carriages and a luggage-van, weight 

 about 41 or 42 tons. The descent was commenced at a speed of about 36 

 miles pel hour — rails dry, and slight head wind. 



In this experiment the velocity down an incline, less by 20 feet per mile 

 than that down which the narrow-gauge trains have never yet maintained a 

 uniform velocity of more than 36 miles per hour, increased from 36'3 to 42 4 

 or 6'1 miles per hour. And yet we have little doubt we shall still find 

 practical men contending for the high rates of resistances which some of the 

 narrow-gauge party pertinaciously assume to be due to all railway trains 

 travelling at high velocities. 



The eleventh experiment was from the 172J to the 170J — viz., two miles. 

 The engine employed was the " Sa'urn," and the train consisted of five pas- 

 senger-carriages and a luggage-van, weighing about 56 or 57 tons. For 

 about two-thirds of a mile the fall is 1 in 82 j this is followed by a fall of 

 about 6 chains of 1 in 90, and another fall of about 7 or 8 chains of 1 in 82. 

 The rest of the distance is on a fall of 1 in 90. The average velocity of the 

 train through the White Ball Tunnel, 40 chains in length, and which imme- 

 diately precedes the inclines over which we took the working of the train, 

 was 4'2-5 miles per hour. It will be seen that this speed was increased to 

 50 miles an hour at the HO-Jth mile-post. 



The twelfth experiment was a second run down the 1 in 120, between the 

 174th to the 176|^th mile-post. The engine employed was the " Firebrand," 

 and the train consisted of four carriages and a luggage-van, weighing about 

 44 or 45 tons — rails dry, and moderate side wind. 



The thirteenth and last experiment was with the " Milo," and a train of 

 three passenger-carriages and a luggage-van. Weight, about 34 or 35 tons. 

 A brisk side wide prevailed. 



In this experiment the steam was shut off at the 1 72| mile-post, which is 

 in the White Ball Tunnel. 



* Qy. seven-sixteenths. 



t Qy. chains. 



REVIEWS. 



Account of the Skerryvore Lighthouse, with notes on the lUmnination 

 of Lighthouses. By Alan Stevenson, LL.B., F.R.S.E., M.I.C.E., 

 Engineer to the Northern Lighthouse Board. Edinburgh : Adam 

 and Charles Black, 1848. 



[second notice.] 



AVhat Mr. Stevenson calls " Notes on the Illumination of Light- 

 houses," may more rightly be called another work, and one not less 

 important nor valuable than the account of the Skerryvore Light- 

 house. Indeed, he calls the former Part II. He begins it bv 

 a short history of lighthouses, in which he shows a gi-eat deal of 

 learning ; and as by the former part every one will see that he is 

 a hard-working man, so by this they will see that a man may be 

 able to understand Homer in Greek, and yet be a good engineer. 



