538 



SCIENTIFIC NEWS. 



[Nov. 23, i£ 



introduced an element of error, which must be variable 

 almost directly in proportion to the extent to which the 

 lever came into play. With a heavily-loaded brake the 

 error must exist ; and with a lubricant which materially 

 lessened the total friction of the wood blocks upon the 

 wheel, it must amount to a considerable part of the 

 whole indicated power, unless adequate allowance was 

 made for it. This allowance had seldom been made. 

 In a better form of compensating brake, designed by 

 Mr. Balk, and used by Messrs. Ransomes, Sims, and 

 Jefferies, the compensating lever was outside, instead of 

 within, the circumference of the brake-strap. It con- 

 nected the ends of the strap, and to its outer end was 

 suspended a scale-pan, and a weight sufficient to keep 

 the lever floating. This weight became a measure of 

 the tension upon the belt, at least at the parts to which 

 it was attached ; but it must be varied with change of 

 condition of the brake-blocks, the lubricant, and the tem- 

 perature of the blocks and wheel ; and it must be taken 

 as acting in favour of the motor. The great advantage 

 of this brake was that the experimenter could always 

 ascertain the actual load, although the tension-lever 

 acted as a compensating lever. There was considerable 

 variation in the scale-weights with the same gross load. 

 This, Mr. H. A. Byng explained, was due to the heating 

 of the brake-wheel. When much heated, more grease 

 had to be used, and in consequence the coefficient of 

 friction was reduced, and the weights in the scale had 

 to be augmented to give more tension in the brake- 

 straps. Figures given appeared to show that the larger 

 the number of revolutions, the smaller the tension for a 

 given total friction, and this inference was supported by 

 experience. Mr. Byng had found that with the higher 

 speeds less weight was required on the scale for a given 

 load, or the higher the speed the less the necessary 

 tension in the brake-belt. By the Balk brake the tension 

 at the ends of the brake-belt was measured directly ; 

 and for accurate trials a higher speed was preferred 

 with less gross load, and with a scale-weight below 

 7 lbs. A water-cooled brake was used by Messrs. Richard 

 Garrett and Sons. The wheel was 5 feet in diameter, 

 and 1 1 inches wide between the flanges within which 

 the wood blocks ran. An annular trough was formed 

 by internally projecting flanges 3-5 inches in depth. The 

 straight form of Appold compensating lever was em- 

 ployed, though under conditions which seldom, if ever, 

 brought it into play sufficiently to affect materially the 

 accuracy of the indication of the brake. Experiments 

 with this brake showed that the water evaporated in the 

 wheel represented tbermodynamically 71 per cent, of 

 the mechanical work done. A brake used by Messrs. 

 J. and H. McLaren had been devised by Mr. Druitt 

 Halpin, M.Inst.C.E. In it the brake-wheel was 5 feet in 

 diameter, and 7 inches in width. Water was constantly 

 supplied to the trough, and constantly taken away by a 

 scoop pipe. Reference was made to a simple form of 

 friction-brake dynamometer, proposed by Professor 

 Thomson, consisting of a cord or rope passed over the 

 upper half-circumference once, or taking one complete 

 turn round a smooth wheel, the one end carrying a load 

 and the other attached to a spring-balance, the rope 

 bearing directly upon the wheel without the intervention 

 of blocks. This brake worked exceedingly well for 

 small powers, and there seemed to be no reason against 

 its use for large powers if a number of separate 

 ropes were used. All the ropes might be attached 

 to a cross-head at either end, from which the weight 



would hang, and to which the spring-balance could be 

 attached. 



The author then proceeded to investigate the tension 

 in the brake-strap, straps, or belt, and the pressure upon 

 the wood-blocks, and considered the effect of the intro- 

 duction of the Appold compensating lever, with the 

 object of ascertaining whether it was a desirable feature 

 or not. Some information on this point, obtained by 

 Messrs. McLaren, was cited, and the paper concluded 

 with an investigation on this subject, for which the 

 author was indebted to the Consulting Engineers of the 

 Royal Agricultural Society of England. 



GEOLOGICAL SOCIETY. 

 At the meeting held on Nov. 7th, 1888, W. T. Blanford, 

 LL.D., F.R.S., President, in the chair, the following com- 

 munications were read : — 



The Permian Rocks of the Leicestershire Coal-field. By 

 Horace T. Brown, Esq. The Author considers that 

 whilst rocks belonging to the Carboniferous and 

 Trias have been mapped as Permian, true represen- 

 tatives of the Permian do exist in the district to 

 a considerable extent. The Bunter Conglomerates 

 rest for the most part upon the truncated edges of 

 Carboniferous strata ; but intercalated between them 

 and the Carboniferous, at various points, are thin beds of 

 purple marly breccias and sandstones, seldom exceeding 

 from 30 ft. to 40 ft., but differing in lithological character 

 from the overlying and underlying rocks. The brecciated 

 series rests with striking unconformity upon the Carbon- 

 iferous. Moreover, the Boothorpe fault, which throws 

 the coal-measures 1,000 ft., affects the overlying brec- 

 ciated series to an extent of not more than from 20 ft. 

 to 30 ft. The unconformity between the brecciated 

 series and the Bunter is less obvious. Sections estab- 

 lishing the double unconformity were described in 

 considerable detail. Attention was also called to other 

 localities within the coal-field where Permian rocks exist, 

 the author having in many cases mapped their boundaries. 

 He further called attention to certain beds which have 

 been erroneously classed as Permian by the Survey. 

 The first of these is a patch at Knowle Hills. Making 

 extensive use of the hand-borer, he found that the greater 

 part of the so-called Permian consists of a wedge-shaped 

 piece of. Lower Keuper let down by a trough fault. The 

 so-called Moira grits belong to and are conformable with 

 the ordinary coal-measures of the district. 



The Author concluded that the Permian rocks of the 

 Leicestershire coal-field belong to the same area of 

 deposition as those of Warwickshire and South Staf- 

 fordshire, all having formed part of the detrital deposits 

 of the Permian Lake which extended northwards from 

 Warwickshire and Worcestershire, and which had the 

 Pennine chain on its eastern margin. He pointed out 

 the dissimilar nature of these deposits to those of the 

 eastern side of the Pennine chain from Nottingham to 

 the coast of Durham. There were proofs of the existence 

 of a land barrier, owing to the uprising of the Carboni- 

 ferous, between the district round Nottingham and the 

 Leicestershire coal-field. He indicated the probable 

 course of the old coast-line of the western Permian 

 Lake. Denudation had bared some of the older Palaeo- 

 zoics of their overlying coal-measures, and it is the re- 

 arranged talus from the harder portions of these older 

 rocks which now form the brecciated bands in the Leices- 

 tershire Permians. 



