May 8, 1884] 



NA TURE 



one foot, a result which will be allowed to be very 

 strongly confirmatory of our previous deduction;." 



In 1844 we have a paper communicated to the Royal 

 Society on "Changes of Temperature produced by the 

 Rarefaction and Condensation of Air." This piper was 

 not accepted by the Royal Society for its Transactions, 

 and the Philosophical Magazine had the honour of pub- 

 lishing it ! In 1845, in a paper read before the British 

 Association, he describes experiments made by stirring 

 water with a "sort of paddle-wheel" in a "can of peculiar 

 construction;" and in 1S46 this was followed by an 

 important paper on " Heat disengaged in Chemical 

 Combinations.'' 



It was, however, in 1849 that his celebrated piper " On 

 the Mechanical Equivalent of Heat" was communicated 

 by Faraday to the Royal Society. This was the first of 

 Joule's papers which was communicated to and not 

 rejected by the Royal Society, and it was rewarded by a 

 Royal Medal ! In this paper he describes experiments 

 (1) on friction of water; (2) (3) friction of mercury, two 

 series of experiments; (4) (5) friction of cast-iron, two 

 series. From all these he concludes : — 



" (1) That the quantity of heat produced by the friction of 

 bodies, whether solid or liquid, is always proportional to 

 the quantity of force expended ; and 



" (2) That the quantity of heat capable of increasing the 

 temperature of a pound ot w iter [weighed in vacuo and 

 taken at between 55° and 6o°] by i° F. requires for its 

 evolution the expenditure of a inech viical force represented 

 by the fall of 772 lbs. through the space of one foot. '' 



In 1867 a report was communicate i to the British 

 Association through the Committee on Standards of 

 Electrical Resistance, containing the results of fresh 

 experiments on the dynamical equivalent of heat. Finally, 

 at the desire of this Committee, and aided by funds 

 placed at his disposal by the British Association, Mr. 

 joule undertook a complete redetermination. This was 

 commenced in 1870, and his report was given in 187S. 

 Here is his conclusion, stated in the last two sentences 

 of the present volume : — 



"The equivalent at the sea-level and the latitude of 

 Greenwich will therefore be 773 492 foot-pounds, defining 

 the unit of heat to be that which a pound of water, 

 weighed by brass weights when the barometer stands at 

 30 inches receives in passing from 6o c to 6i° F. With 

 water weighed in vacuo the equivalent is finally reduce i 

 to 772-55-" 



It is impossible for us to do more here than mention some 

 of the other papers contained in this volume. Perhips 

 among those which are of highest importance we should 

 refer first to a short piper " On the Theoretical Velocity 

 of Sound," in which outstanding difficulties are cleared 

 up, and deductions as to the true relation between the 

 specific heat of air, volume constant, and the specific heat, 

 pressure constant, are brought forward. We have also 

 important experiments on " Some Amalgams," in which 

 their mcde of production and characteristics are dealt 

 with A paper " On Surface Condensation of Steam " wis 

 largely conducive to the great improvement which the 

 substitution of this method, for condensation by injection, 

 has realised in the condensing engine of the present day. 



In connection with his very earliest work Joule gave 

 special attention to the construction of thermometers. 

 He was the first to produce accurate thermometers in 



England, as Regnault did, just about the sane time, in 

 France. Joule's thermometers were made for him by 

 Mr. Dancer of Manchester. In 1S67 we hive a paper 

 "On the Alteration of the Freezing-Point," giving the re- 

 sults of the observations of five and-twenty years on this 

 curious phenomenon. In the present volume the paper 

 is supplemented by observations carried down to Decem- 

 ber 1SS2. 



We mention, lastly, his papers describing experiments 

 1 1 test the brittleness supposed to be imparted to iron 

 castings by frost — experiments which, so far as they go, 

 negative altogether the popular idea on the subject ; and 

 with this mention we must take our leave of the volume, 

 expressing once more our deep appreciation of its value, 

 and earnestly hoping for the speedy appearance of its 

 promised companion. 



LETTERS TO THE EDITOR 

 [ The Editor does not hold himself responsible for opinions expressed 

 by kis correspondents. Neither can he undertake to return^ 

 or to correspond with the writers of, rejected manuscripts. 

 No notice is taken of anonymous communications. 

 [The Editor urgently requests con espondents to keep their lettets 

 as short as possible. The pressure on his space is so great 

 that it is impossible otherwise to insure the appearance even 

 of co m ',. unications containing interesting and novel facts. ] 



Long or Short Fractions for Great Natural and 

 National Standards — Earth's Axis of Rotation 



In the two last numbers of the American School of Mines 

 Quarterly fournal the learned President Barnard of Columbia 

 College, New York, has involuntarily opened a question of far 

 wider interest than the particular one with which he set out. 

 For on his page 120 there stands the following remarkable 

 statement : — 



"The length of the polar axis of the earth is a quantity which 

 may with strict truth be pronounced to be, up to this time, 

 absolutely unknown." 



Now if that really be so, the peoples of every civilised country 

 on the face of the earth, who have been taxed during the last 

 hundred years to the extent of millions and millions for the sup- 

 port of magnificent arc-of-the-meridian measuring establishments, 

 have some right in common sense to rise with revolutionary wrath, 

 and demamfhow those enormous sums of their money, given to 

 determine the size and shape of the earth, have been expended. 

 And when shall we know the far greater distance of the sun '. 



But the statement can only be true on some private interpreta- 

 tion which is needless to inquire into ; for when we take the 

 various lengths of the earth's axis of rotation as determined in 

 modern times, and collected by President Barnard himself from 

 very diverse sources indeed, we find them all to be coincident to 

 four places of figures at least. And considering that for some 

 other most important natural standards the world is apparently 

 content with a certainty of two places of figures only, the officers 

 of the several trigonometrical establishments of all the countries 

 of Christendom deserve high praise, rather than blame, for the 

 results they have succeeded in bringing out. 



The mean of their last five measurements, as given by 

 President Barnard for the polar axis of the earth, is 



503,492, 732^8 British inches, 

 the ten-millionth part of which is evidently 



50-04927328 British inches ; 

 though he has chosen to bring it out as a very different quantity 

 indeed, viz. 49-273 British inches. 



But the rather important point now to be discussed is, whether 

 in practical use as a standard of measure, either on paper or for 

 mechanical work, we should attempt to realise that long fraction ; 

 or be content with the 



50 '05 British inches, 

 at which, as quoted by the President, I had years ago ventured 

 to assume the said ten-millionth of the earth's axis of rotation. 



In place of merely, and perhaps vainly, theorising on the sub- 



