Nov. 23, 1888.J 



SCIENTIFIC NEWS. 



537 



tage composition of the saliva. Thus an insufficiency of 

 oxygen, as in dyspepsia, decreases the rate of secretion 

 ot saliva, but the saliva has a higher percentage of salt?, 

 and usually a higher percentage of organic substance. 

 Loss of blood also decreases the rate of flow of saliva, 

 but very markedly increases the percentage of organic 

 substance. The dilution of the blood by sodium chloride 

 solution - 2 to "6 per cent, leads to a much more rapid 

 flow of saliva, but the percentage of salts in this saliva 

 falls, instead of rising. If, however, strong salt solution 

 is injected into the blood, the percentage of salts in the 

 saliva rises somewhat. 



It appears then from these experiments that the 

 character of saliva is determined by (1) the strength of 

 the stimulus, (2) the character of the blood, (3) the 

 amount of blood supplied to the gland. 



Messrs. Langley and Fletcher point out concerning the 

 theory of secretory nerves, that " nearly all the argu- 

 ments which have been adduced to prove that the secre- 

 tion of organic substance is governed by special nerve- 

 films have their counterparts with regard to the secretion 

 of salts, so that we might imagine at least three kinds of 

 secretory films to be present. The experiment?, on the 

 whole, indicate that this complicated arrangement does 

 not exist, but that the stimulation of a single kind of 

 nerve-fibre produces varying effects according to the 

 varying condition of the gland cells." 



THE INSTITUTION OF CIVIL ENGINEERS. 

 At the meeting held on Tuesday, the 13th of November, 

 the President, Sir George B. Bruce, being in the chair, the 

 proceedings commenced with the distribution of the 

 medals, premiums, and prizes awarded by the Council at 

 the close of the last session. 



A paper on " Friction-Brake Dynamometers " was then 

 read by Mr. W. Worby Beaumont, M.Inst. C.E. The 

 author stated that the indications of any apparatus de- 

 pending on friction must be as variable as the causes of 

 friction and the conditions affecting it, and hence the 

 value of the measurements, obtained by means of a 

 friction-brake dynamometer, must depend on the com- 

 pleteness with which these causes and conditions were 

 taken into consideration or were eliminated. In a 

 friction-brake, the causes of friction were similar to those 

 which generally obtained in other applications of 

 materials brought into rubbing contact; but the con- 

 ditions were more variable, and chiefly due to variation 

 in pressure and in lubrication, both being affected by 

 the rate of work-absorption and temperature. The 

 friction-brake dynamometer in nearly all its forms was 

 essentially that devised by Prony. In it the friction 

 between a system of wood blocks and the surface of a 

 wheel rotated by the motor whose power was to be 

 measured, was employed in maintaining a weight, 

 suspended at a point on a horizontal line, level with the 

 centre of the wheel. For most practical purposes, this 

 brake was capable of sufficiently exact determinations 

 of power, ranging from 5 to 200 h.p., but it presented 

 some of the elements of inaccuracy which pertained to 

 the friction type of absorption-dynamometers, especially 

 when used for the measurements of variable powers. 

 For measuring the power of a motor, capable of running 

 at a uniform speed with a constant load, the inaccuracy 

 of its indications might be very small and often quite 

 insignificant. With a truly circular wheel and uniform 

 turning power, this brake gave very nearly accurate 



results, provided the lubrication was regularly main- 

 tained ; but slight variations in this respect, due to 

 variation in quantity, quality, and temperature of the 

 lubricant and rubbing surfaces, made it difficult to keep 

 the tension of the strap in strict accord with the total 

 friction necessary to maintain the load at a constant 

 level. The frequent change of this tension by the 

 screws, for the purpose of meeting these variations, in- 

 troduced further inaccuracy. 



A simple form of friction-brake, much used as a 

 dynamometer for testing engines by running them against 

 a known load, consisted simply of a thin iron or steel 

 strap, or a pair of straps, to which were attached a 

 number of blocks of wood. A hook was fastened to the 

 straps for the suspension of the load, and the ends ot 

 the strap were connected by a right-and-left-handed 

 screw for the adjustment of the tension on the strap or 

 pressure of the blocks upon the wheel, so as to obtain 

 the necessary frictional grip to carry the otherwise un- 

 supported load. With a truly turned wheel, and with 

 uniform lubrication, this brake would run for hours with 

 a variation of but a few inches in the level of the load, 

 if the engine was of good design and had a proper fly- 

 wheel. The variations from several causes were, how- 

 ever, sufficient to make adjustment by the hand-screw 

 necessary, sometimes frequently. The errors in esti- 

 mating the work done by the engine, which resulted 

 from these causes, were generally small ; but it was 

 desirable to remove them for very accurate tests. It 

 had been with this object that devices, for automatically 

 varying the tension in the belt with the variation in the 

 total friction, had been introduced. At an early date a 

 brake-wheel, with an internal water-channel, was used 

 to avoid the mechanical difficulties which resulted from 

 the heating of the brake-wheel, and the variations due to 

 the heating of the lubricant. One form of automatically- 

 adjusting or compensating brake, suitable for small 

 powers, was due to Mr. Deprez. A simple self-adjusting 

 brake dynamometer had been devised by Mr. J. Imray, 

 M.Inst. C.E. In this, the compensating action was due to 

 the increase in total friction which accompanied increase 

 ot circumferential surfaces in contact. A modification 

 of this brake consisted simply of a belt provided with 

 wood blocks, but bearing only on the upper half of the 

 circumference of the wheel. At one end of the strap 

 was the load to be lifted by the motor, and at the other 

 end was a spring under sufficient tension to give rise to 

 enough friction to enable the motor to lift the load. 

 This arrangement was very simple and useful. One 

 of the best known friction-brake dynamometers, fitted 

 with a compensating device, was that designed by Mr. 

 C. E. Amos and Mr. Appold, used for the larger powers 

 by the Royal Agricultural Society. Besides the hand- 

 adjusting screw, it was provided with a compensating 

 lever, by means of which the rise or fall of the load was 

 attended with a decrease or increase in tension on the 

 brake-strap, so that a position of equilibrium was auto- 

 matically attained without causing inaccuracy in the 

 indications. The compensating action could not, however, 

 come into play except by the rise or fall of the weight 

 from its proper position, and hence the value of the 

 device was confined to its power of limiting that rise and 

 fall. In practice, generally speaking, the adjustment 

 required by means of the screw was as necessary with 

 the compensating lever as without it, and its value 

 might therefore be questioned for this reason alone. A 

 further objection to this compensating lever was that it 



