That wonderful little pumping engine which we all carry around in our bosoms, and which runs without cessation till death ruthlessly closes the throttle, performs an amount of work so great as to be almost beyond belief till substantiated by arithmetical calculation. If we scrutinize the mechanism of the heart, we shall find that it involves in its operation nearly all the principles of hydrodynamics. It may, therefore, be brought within the domain of mathematics as well as any other machine. In the attempt to calculate the power of the human heart for a given time, we shall arrive at some curious and interesting, not to say astonishing results. Few would credit, at first, the statement that the hearts now beating in and around the city of New York, exert an aggregate power ample to propel a large steamer across the Atlantic ocean at a fair rate of speed, yet we shall be able to demonstrate that this is as much a fact, as that any of these steamers ever crossed that storm-torn sea. Blood is heavier than water; its specific gravity being, ac cording to Booth, of from 1'0527 to 1'057. For convenience, however, we shall consider it as being of the same weight as water, extreme accuracy not being essential to our purpose and in our computations we shall, for the most part and for the same reason, throw out fractions and use round numbers. The pressure required at the mouth of the aorta to force the blood through the vessels of the human body, is estimated by Hales, as being equal per square inch of surface, to that exerted by a col umn of blood seven and one half feet high. The pressure per BfJiiaro inch was esthnmtoil by Poi- S4)uillc as four pounds three ounces. Others have estimated tho pressuro as that of u. column of water six feet in hight. The results vary in (iflorent experiments, but they arc sufficiently accurate to give us an average that wo may rely upon as within bounds. They are also something more than lucre estimates, as this pressure has been measured by pres. sure gagcs inserted into tho blood vcasels. Wc shall consider the pressure as that of a water column six feet inliight, the weight of which would be nearly forty- two ounces, which, for simplicity, we will consider forty-two ounces, or two pounds ten ounces avoirdupois. Tho svemge discharge oftlie heart at eM.i pulsation may be estimated atono amdono half ounces.and itsnumberof beats nt «eventy-five per minute ; waking au aggregato of 112 ounces, or seven pounds dischanged per minute. The anrnge internal diameter of the aorta, or the gre;,t artery through which the blood passes from tho heart into tho general circulation, may be taken asbeiug in adults three quarters of an inch. Seven pounds of bleed per minnte is therefore forced through this artery against a pressure of forty-two ounce!, equivalent to raiding seven pounds six feet each minnte, equal to raisiug forty-two pounds one foot, or forty-two footpounds. From tlie diauioier of the aorta and the amount of blood forced through it we might compute the elocity of flow, but ihat is not easential to our purpose. AU consideration of friction in the porformanco of this woii is also omitted, so that tlw estimate of forty-two foot-pounds per m inute must cons'Gered as considerably less thl\n the actual work performed, this result corresponding to what is called useful work in the performance of macliincs. Forty years of this work would be equo.l to the work of twenty-six thousand seven hundred anil fifty-sew:i horses for one minute of time, or the work of' one horse for forty-four IWd one half days 'Jf ten hours. Tlie work of seven huudred r.nd eighty-six adult hearts is “(j ual to oiie-horse power ; therefore seven hundred and tigiilysix thousand hearts would pcrform the work of one l housand ho rs 'S. The 14:'giegato population of New York. Brooklyn. and Jersey City, was, according' to the census of 18G:), on” million one hundred and twenty-two thousand, and it may be safe!? cstinmteil llow nt one and one half mill ions. Considerijig this Ils equal to ait adult population of twelve hundred thousand, their united lieart-beats cxcrt it power equal to that of one thousand fivo hun:ircol and twenty-scven liorses. Avoragitig tie power ef the united pulsations of adults and children as equal to that of four fifths the ontire population, and taking the census of 18(;0 as n basis for calculation, tho work done by all tlu; human hearts in tlio United States nearly equals that of thirty-two thousand horses. The work done by the boating of all the human hc><rts on the globo is equivalent to the power of ono million forty- six thousand and fifteen horses, The nominal liorse power of the engines in the Gre.it ^nato'ii is fonr thousand; considering tiie actual horf!(J power to be ten thousand, the power exerted by the tinited human heart-beat of til.., world is sufficient to propel a flLeot of ono hundred and four Ureat rrn.'s at fnll speed continually. This power could only be generated in average steam engineering practice by the combustion of feu- thousand six hundred lind eighty tuns of cv.nl per hour. When \\'e reflect tliat the human family is small in comparison ev “i with tics great class of mammalia, of which it formsa part, and that lusIly of tho same elass, as the whale. the elephmnt, the rhinocerous, hippopotamus, giraffe, etc., have hearts of very much greater size and power than the human heart; nnd when we conceive of tiio enormous additional work performed Iiv the hearts ofreptiles,birds,fishes, molltisks, and insets, ami to ths work add in imagination the power expended in tilt movement of the respiratory appa. ratus of animals, and voluntaiy rnuscul ar movement, ncees- Mry to obtain sustcnenco for theso animals, we may gain some feeble conception of the enormous expenditure of mc- chauical power required to sustain animated existence on the earth.