Til 



DYXAMOMKTKK. 



I'YSKXTERY. 



711 



power OMd to set iuch machine in motion were applied to D, the 

 pring would maintain a flexure eoi responding to the resistance open- 

 ting on c, and a* this resistance varied from one moment to another, so 

 would the flexure of the spring vary to accommodate iUslf to the 

 working (ore* which WM actually passing through the dynamometer. 

 Now, U mean* were contrived for accurately recording the varying 

 flexure* of the spring, we ahould have a complete indication of the 

 varying power expended during any given time, during which the 

 m^viwi to I* examined wa under trial. To accomplish this, there is 

 attached to the boat which hold* the heel of the spring E, a frame-work 



{, which supports a series of roller g k i, a fusee J, and a pencil holder 

 , while on the edge of the pulley o is a second pencil-holder /. In 

 using the dynam<imeter a long ribbon of paper U wound on the roller 

 A, and its outer end being carried over the roller g is made fast to i. 

 The roller i is driven by a string paaiing from it over the fusee J, 

 which bears on its axis a wheel m, in gear with another wheel n, 

 situated on the axis A. It will be seen that when by the revolution of 

 the dynamometer axis the wheel m is turned, the string will gradu- 

 ally wind upon the fusee J, and the paper will be drawn from the 

 roller A over g, and be coiled upon i. The use of the fusee and string 

 is to give a uniform rate of motion to the paper, notwithstanding the 

 continually increasing diameter of the cylinder i, upon which it is 

 being wound. The two spring pencils, I- and /, are so adjusted that their 

 points may press lightly on the paper-ribbon, and so long as the spring 

 i remains unbent, the pencil poinU are exactly opposite to each other, 

 and they trace only a single line on the paper. The teeth of the 

 wheels m and * are cut slantingly, so that one will drive the other 

 when placed in planes perpendicular to one another. These details 

 being understood, let the dynamometer be set in action, and the 

 spring c being more or less bent, the pencil-point I will be carried to 

 the right or left of t, and as the paper is drawn under these pencil 

 points by the action of the string winding upon the fusee J, the pencil 

 i on the frame / continues to trace a straight line on the paper, while 

 the other pencil / attached to the wheel, traces a curved line at dis- 

 tance* from the straight line varying exactly as the flexure of the 

 spring, and therefore exactly as the driving force transmitted by 

 the dynamometer varies. There is a contrivance by which the 

 observer can in an instant, engage or let free the toothed wheel n, so 

 as to make it drive the other wheel m, which gears into it, or when let 

 free the two wheels are simply carried round by the axis, without any 

 relative motion. The observer then allows the paper to move during a 

 given period, which may comprise a certain number of seconds, or a 

 given number of revolutions of the wheel, or a certain number of 

 strokes of a steam-engine. When the experiment has been made the 

 machine is stopped, and the paper unwound. Now it ia evident that 

 the lengths of the lines traced by the pencil points bear a certain 

 definite ratio to the space through which the circumference of the 

 pulleys has moved ; that is, the space through which the driving force 

 has acted ; while the distance of the two lints asunder, bears at every 

 moment, a definite proportion to the intensity of the force which has 

 been pi using through the machine. The first of these is the measure 

 of the abscissa of the curve traced, while the ordinate of the curve 

 drawn at any part, represents the force acting at the corresponding 

 moment of the experiment. Hence the area of the curve gives the 

 product of the amount of force acting continually by the space through 

 which it acts ; that is to say, it gives the exact quantity of wont which 

 has passed through the dynamometer into the machine under ex- 



A corresponding observation having been made of the 

 useful effect yielded during the same period, such as the number of 

 pounds of water raised to a given height, an exact measure is obtained 

 of the ratio of these two results, and the duty of the machine under 

 examination is accurately determined. 



There is another mode of registration, in which the wheel n, instead 

 of driving a fusee is made to turn a small plane disk covered with hard 

 leather. The edge of a small wheel presses lightly on this disk, and 

 attached to the axis of the wheel is a registering train like that of a gas 

 meter. The leather disk is attached to the frame /, and the steel 

 wheel to the pulley o. The wheel ia so adjusted that when the spring 

 is not bent, the edge of the wheel shall press exactly on the centre of the 

 disk, so that in this position the disk, when driven by the wheel n, has 

 no tendency to turn the steel wheel ; but when the spring ix bent, the 

 steel wheel is moved from the centre of the disk towards the circum- 

 ference, and the friction thus produced between its edge and the 

 surface of the disk causes the steel wheel to be driven at a greater or 

 lev speed, according to the relation between its own diameter and the 

 diameter of that circle on the disk on which its edge may happen to be 



, In this way the extent of rotation of the steel wheel ia a 

 of the product of the intensity of the acting force by the 



1. which it acts, and this being registered during any 



. gives one of the values required for the determination of 

 > duly sought. 



This apparatus is remarkably accurate in its results : it can be 

 readily applied to any machine, so as to furnish the most valuable 

 information both to the maker and to the employer of machinery. 

 Every set of observations made with this dynamometer furnishes a 

 manufacturing eoutoul of great value in determining the cost of pro- 

 duction under widely different circumstances. The instrument has 

 been used for determining the power transmitted by machinery from 



^team-engines and water-wheels, and also for ascertaining the value of 

 manual labour as applied to the working of pumps and driving machi- 

 .. cranks. It has also been applied to estimate the traction of 

 hones ; and every effort of a team through successive days of labour 

 has been measured and recorded, and the work expended on such 

 efforts numerically estimated. In comparing the various modifications 

 of machines, some surprising differences in the results have been 

 attained, showing how very important it is that the use of this instru- 

 ment ahould be more widely extended. The special circumstances of 

 each case may require modifications in iU form, and in measuring 

 forces of high intensities additional springs may be required in the 

 other sides of the boss, and connected with the pulley n. In the Great 

 Exhibition of 1851 were various forms of dynamometer, some of 

 which are noticed in the ' Jury Report,' Class X., and also Claw V . 



DYSENTERY (Awrcrrtpfa, dytenterio, from tut, vith dijKrulty, and 

 trrtpoir, inttttint ; dijKfultoi inltttinorum, bloody jinx), a dincnsn in 

 which there U difficulty and pain in p*j""K the stools, which consist 

 of mucus and blood, containing little or no feculent matter, and gene- 

 rally attended with fever. The desire to evacuate the bowels is 

 frequent and urgent ; but the effort is accompanied with severe pain, 

 and is often altogether ineffectual, constituting the affection called 

 tenesmus. What scanty stools are passed consist, as has been stated, 

 of mucus mixed with blood, or of pure blood in considerable quantity ; 

 and if any fa-culent matter be present, it is commonly in the form of 

 round and hard balls called scybahc. There is always griping pain in 

 the abdomen. More or less fever is invariably present. The seat of 

 the disease is chiefly in the minute glands of the mucous membrane of 

 the large intestines, and is essentially of an inflammatory character. 



The forms of this disease, the causes which produce it, the cin inn 

 stances under which it prevails, the pathological conditions on which 

 iU essential characters depend, and its degree of intensity, are infinitely 

 various; and these modifying influences cause it to assume at dif- 

 ferent seasons, in different climates, and in different constitutions, the 

 most diversified aspects. It is sometimes a primary, sometimes a con- 

 secutive, and sometimes a symptomatic disease. It is now sporadic, 

 now endemic, and occasionally both endemic and epidemic, it in 

 sometimes inflammatory and stbenic, at other times typhoid and 

 asthenic, at one time acute, and at another chronic. These differences 

 are attended with essential differences in the nature of the disease, 

 which not only communicate to it different external aspects, dependent 

 on different internal conditions, but which require totally ditl'.-n-nt 

 remedies. 



This disease has been at all times one of the great scourges of our 

 fleets and armies. It occurs equally in hot and temperate climates, 

 and seems to depend more on irregularities of diet and habit than on 

 climate. "During the Peninsular war, the first Burmese war, and 

 the late war with Russia, dysentery was one of the most prevalent and 

 fatal diseases which reduced the strength of the armies." 



In the acute form of dysentery, when purely inflammatory. and 

 when mild in character, constipation commonly precedes for some ilay- 

 tlie attack of diarrhoea. The liquid and frequent stools which at 

 length succeed to this state of constipation soon become streaked 

 with blood; the griping pains which accompany the evacuations, and 

 the straining and tenesmus which follow them, are often ati 

 with distinct chills. The stools may be from eight or ten to sixteen 

 or twenty in the twenty-four hours. The pulse is commonly quick 

 and small, the tongue loaded, and the appetite little impaired. 



When the attack is more severe, it is generally attended at the very 

 commencement with diarrhoea, often accompanied with nausea and 

 vomiting, quickly succeeded by scanty, mucous, or gelatinous stools, 

 streaked with blood, preceded by tormina, and followed by tenesmus. 

 The pain in the course of the large intestines may be either severe, or 

 it may not be urgent, but rather a sense of heat and aching than 

 acute pain. Pain, however, is always induced by full pressure over the 

 tract of the colon ; and if, in any [articular part 'of this tract, there be 

 urgent pain, some degree of fulness* may generally be perceived tlu n . 

 The progress of the disease is indicated by the increasing severity of 

 all the symptoms, and more especially by the increasing frequency of 

 the stools, by the increasin^tormina and tenesmus, and the augim -nta- 

 tion of the general febrile symptoms'. It is not uncommon for from 

 twenty to forty efforts at stool to be, - *i in the twenty-four hours, 

 with the effect of passing only a very i-.u: quantity of mucus and 

 blood. In all cases the evacuations are ex" xlingly offensive ; in the 

 worst they are of a cadaverous odour, and the clots of blood are 

 sometimes mixed with pieces of coagulated lymph or fibrin. 



In hot climates the disease is still more intense. The heat, the 

 tormina, and the tenesmus, are more urgent and distressing; tin- 

 thirst becomes excessive, the urine scanty or altogether suppressed, the 

 stools slimy, streaked with blood, and attended with prolapiaf 

 watery and ichorous, " resembling the washings of raw beef, in \\hirl, 

 Boat particleti or even large shreds of coagulable lymph, thrown off 

 from the acutely-inflamed surface." In these cases the prostration of 

 strength ia extreme, and is increased by most distressing and exhaust- 

 ing voinitiiiK. When, as sometimes happens in this form of the 

 disease, portions of the mucous coat of the intestine slough away, tho 

 countenance of the patient is sunk and cadaverous, and the odour 

 of the stools, and in some degree, indeed, of the whole body, U 

 putrid. 



