DYNAMOMETER. 



299 



rcxui. 



fift. 3. 



J:;. 4. 



tig. 3. 



F4g.6. 

 Kg- 7. 



Fig. f. 

 Fig. 9. 



MS. This spring is covered with leather to prevent it 

 from hurting the fingers when strongly pressed with 

 the hands. It is composed of the best steel, excellently 

 welded and tempered, and subjected to a greater force 

 than it ever can be exposed to when in use, in order 

 that it may not lose any of its elasticity by frequent use. 

 A piece of steel B, Fig. 3. is firmly fastened to the 

 spring by means of a claw and screws, and is intended 

 to support a semicircular plate of brass C, Fig. 2. for 

 receiving the scales or graduated arcs. The outermost 

 of these arcs is divided into myriogrammes, and the 

 other into kilogrammes. Each of these arcs is still far- 

 ther subdivided by points, which express the weight in 

 pounds marc ; and the various parts of the scale are de- 

 termined experimentally, by appending accurate weights 

 to one of the extremities of the elliptical spring. On 

 the other branch of the spring, is a small steel support 

 I), furnished with a horizontal cleft at its upper extre- 

 mity, to receive freely a small copper lever E, which is 

 kept in its p'ace by a steel pin a. This part of the 

 machine is represented on an enlarged scale in Fig. 4. 



In the centre of the semicircular plate C, ( Fig. 2.) a light 

 steel index F is fixed upon its axis by a screw, and has a 

 double point, viz. at m and n, for indicating the divi- 

 sions on both scales. A small piece of leather, or cloth, 

 is glued upon the lower side of the circular part C, to 

 render uniform, and diminish the friction on the plate. 

 The point m of the index, and the scale of myriogrammes 

 is employed in all experiments, in which the spring is 

 to to be pulled in the direction of its greater axis AA, 

 and the point n and the scale of kilogrammes is used, 

 when it is to be employed for experiments in which the 

 two sides of the spring are to be compressed. 



The mechanism now described is covered with a 

 small plate of brass CD, Fig. 5, to prevent it from bt 

 ing injured. I'pon this plate is a divided arc, corre- 

 sponding with the fir^t arc of the machine, and by the 

 play of a small index b (Fig. 4.) under the plate, the 

 movements of the spring may be ascertained. Through 

 the aperture K, a s mall tumscrew is introduced, for the 

 purpose of relieving or tightening the index, when ne- 

 cessary. 



A pallet of brass L, Fig. 3. has a screw, with a cap 

 like that on the needle in the mariner's compass, in which 

 the lower pivot of the lever that pushes round the in- 

 dex is made to play. This pallet, acting like a spring, 

 yields to any sudden concussion, and prevents the me- 

 chanism from being deranged. M (Fig. 5.) is a socket 

 rivetted on the plate CD, in which the upper pivot of 

 the lever turns. N, N, N, are small cylindrical pillars, 

 to which the plate CD is fixed by three screws. 



When it is intended to try the strength of the hu- 

 man body, it is necessary to have an iron rack, Fig. 6. 

 on the lower part of which the feet of the person must 

 rest ; and also a double handle of wood, with an iron 

 hook, Fig. 7. which he must at the same time hold with 

 both his hands. 



When the strength of animals is to be determined, it 

 is necessary to have a double iron hook, shewn in Fig. 

 8. one end of which is to be hooked to the end of the 

 spring, and the other to a rope fixed to a stake, as at 

 c, c, Fig. 9. 



The three methods of using the dynamometer, are re- 

 presented in Fig. 9, 1 0, and 1 1 . 



Fig. 9. represents the method of applying the dyna- 

 mometer, to ascertain the strength of animals. The ani- 

 mal is yoked to the chains PQ, and the force which it 

 exerts against the fixed obstacle R is shewn by the in- 

 dex of the interposed dynamometer T. The pin rf, Fig. 4, 



Fig. 11, 



pushes forward the index, which always remains at Dynanw- 

 the place to which it is brought. M. Kegnier made 

 experiments with four excellent horses, and obtained the 

 following results : CCXLII. 



Myriogrammes. Fig- 9. 



Force exerted by the first . ... 56 



second . . . 38 



third . . . . 26| 



fourth ... 43 



4)141 



Mean result 36 



which is equal to 73G pounds marc. 



Fig. 10. shews the method of determining the strength Fig. it'. 

 of the hands, or the muscular force of the arms. The 

 person lays hold of the two sides of the spring nearest 

 to the centre, so that his arms may be a little stretched 

 and inclined downwards, at an angle almost of 45 de- 

 grees. This position is considered by Hegnier as the 

 most natural, and as that in -which a man can exert his 

 whole force. The index will then point out on the 

 scale of kilogrammes the force which has been exerted. 

 The strength of each hand may be tried separately, and 

 the sum of the two will always be found equal to that 

 of both when exerted together. 



Fig. 11. represents the method of measuring the 

 Strength of the reins of the human body. The person 

 places his feet on the bottom part of the rack, shewn 

 separately in Fig. 6, after one of the ends of the spring 

 has been placed in one of the hooks of the rack, and 

 the hook of the handle, Fig. 7, put into the other end 

 of the spring. The strength which he exerts in this 

 position is then indicated upon the scale of myrio- 

 grammes. 



The preceding dynamometer is obviously an instru- 

 ment of great use ; and as it does not weigh more than 

 two pounds and a half, there are few practical purposes 

 to which it may not be conveniently applied.^ For 

 cases, however, where the load or the resistance is sta- 

 tionary, as in those represented in Fig. 9, 10, and 1 1, we 

 think that a much simpler and more accurate dy nano- 

 meter might be constructed in the following manner. 



Let ABCD be a vessel containing water, and EF a 

 long cylinder, made of any substance heavier than 

 water, suspended in the fluid by a rope GH1 attached 

 to the hook G, and passing over a pulley H. When the 

 upper surface E of the cylinder is on a level with the 

 surface of the water, the weight of the cylinder, or the 

 force which it exerts upon the rope GHI, will be equal 

 to the absolute weight of the cylinder in air, diminished 

 by the weight of a quantity of water of the same magni- 

 tude as the cylinder. When a horse or a man pulls at the 

 rope I H, so as to raise the cylinder above the fluid sur- 

 face, the weight of the cylinder will gradually increase; 

 and if the magnitude and specific gravity of the cylinder 

 are duly adjusted to the description offeree which is ap- 

 plied, there will be a particular position of the cylinder, 

 at which its weight will exactly balance the force which 

 is applied at I. The forces which are then in equilibrio, 

 or the ft rce required to be measured, will be equal to 

 the absolute weight of the cylinder diminished by the 

 weight of a quantity of water equal to the magnitude 

 of the immersed part of the cylinder. In this way the 

 force of men and animals, and of particular parts of the 

 human body, may be ascertained with the utmost ac- 

 curacy and facility ; and by fixing a scale upon the 

 cylinder, the measure of the force in cwts. or pounds 

 may be seen by simple inspection. The length of the 



New dy*. 

 mometer 

 proposed 

 by l)r 

 Brcwstcr. 



Fig. It. 



