2 2 



NA TURE 



[November i, i960 



Smith and Beck (now Messrs. R. and J. Beck, Ltd.). In the 

 summary of recent researches in microscopy is an interesting 

 ■description (with illustrations) of a microscope, with its oculars 

 and objectives, used by Prof. Amici, the discoverer in 1841 of 

 the part played by the pollen-tube in the fertilisation of flower- 

 ing plants. Nothing ^ould more forcibly illustrate the enormous 

 advance made during the past sixty years in the manufacture of 

 the microscope and its appliances. 



Bollettino della Societa Sismolo^ica Italiana, vol. vi. 1900- 

 1901, Nos. 2 and 3. — On the necessity and on the choice of com- 

 parable seismic apparatus, by A. Cancani (see pp. 395-6).— On 

 the velocity of propagation of the Emilian earthquake of March 4, 

 1898, by G. Agamennone. The velocity is found to be about 

 3 icm. per second, and it does not vary perceptibly with the 

 distance from the epicentre. — Contribution to the study of the 

 great Neapolitan earthquake of December 1857, by L. Antonio. 

 Contains a copy of a letter written from Caggiano, close to the 

 position assigned by Mallet to the epicentre. — New type of seis- 

 mometrograph, by G. Agamennone. A reprint of a paper de- 

 scribing an instrument specially designed for registering the very 

 small movements of the ground, — Notices of earthquakes 

 recorded in Italy (March 21 to June 5, 1899), by A. Cancani, 

 the most important being the Greek earthquakes of April 6, 15 

 and May 3, the Dalmatian earthquake of May 15, and distant 

 earthquakes on March 3, April 2, 12, 13, 16, May 8 and June 5. 



SOCIETIES AND ACADEMIES. 



London. 



Royal Society, June 21. — "On the Capacity for Heat of 

 Water between the Freezing and Boiling Points, together with a 

 Determination of the Mechanical Equivalent of Heat in Terms 

 of the International Electrical Units." Experiments by the 

 Continuous-flow Method of Calorimetry performed in the Mac- 

 donald Physical Laboratory of McGill University, Montreal. 

 By Howard Turner Barnes, M.A.Sc, D.Sc, Joule Student. 

 Communicated by Prof. H. L. Callendar, F. R.S. 



At the Toronto meeting of the British Association in 1897, a 

 new method of calorimetry was proposed by Prof. Callendar 

 and the author for the determination of the specific heat of a 

 liquid in terms of the international electrical units. At the 

 Dover meeting in September, 1899, some of the general results 

 obtained with the method for water over a part of the range be- 

 tween 0° and 100° were communicated, with a general discussion 

 of the bearing of the experiments to the work of other observers. 

 In the present paper the author gives a summary of the complete 

 work, in the case of water, to determine the thermal capacity at 

 different temperatures between the freezing and boiling points. 



Theory of the Method. 

 If a continuous flow of liquid in a tube be made to carry off" a 

 continuously supplied quantity of heat EC, in electrical units, 

 then after all temperature conditions have become steady 



j5Q(0i - %)t +(61-^0) ht = ECif 

 where 



J = mechanical equivalent of heat, 

 Q = flow of liquid per second, 

 s = the specific heat of the liquid, 



6q = the temperature of the liquid flowing into the tube, 

 ^i = the temperature of the liquid flowing out of the tube, 

 A = the heat loss per degree rise of temperature from the 



liquid flowing through, 

 t = the time of flow. 



In the case of water, E represents the E.M.F. across an elec- 

 trical heating conductor in the tube, and C the current flowing. 

 In this case, which is treated of entirely in the present paper, Js 

 is replaced by 4*2 (i + 8) where 5 is a small quantity to be de- 

 termined, and varies with the thermal capacity of the water, 

 which is not exactly equal to 4*2 joules at all points of the 

 Tange. 



Substituting in the general equation, rearranging terms, and 

 dividing through by t, the equation is given in the following 

 form : — 



4-2Q(ei-0o)5 + (ei-eo)/5 = EC-4-2Q(ei-eo), 

 •which is termed the general diff'erence equation of the method. 

 The two terms 5 and h may be determined by using two values 

 of Q, giving two equations of the form 



.4-2Qi(ei + 60)81 + (01 - eo)h = EiCi - 4-2Qi(ei - ^o) 



4-2Q^{e^-eo)s^+{e2-eo)h = E2C2-4-2Q2(e2-»o)- 

 NO. 1618, VOL. 63I 



For the same value of 6^, if the electrical supply for the two 

 flows is regulated so that 61 — 62, then Sj = 83 = 8, and by 

 eliminating h, 



( EiQ - 4-2Qi(gi - Sq)) - (E2C2 - 4-2Q2(ei - ^o)) 



^- 4-2(Qi-Q2)(fli-eo) 



which corresponds to the mean temperature 



where (d-y - ^o) is not too great. 



In the present method the flow tube is of glass, about 2 mm. 

 in diameter, connected to two larger tubes forming an inflow 

 and an outflow tube, in which the temperature of the water is 

 read, by a differential pair of platinum thermometers, before 

 and after being heated by the electric current. A glass vacuum 

 jacket surrounds the fine flow tube and a part of the inflow and 

 outflow tubes, to reduce the heat loss as much as possible. A 

 copper water jacket encloses the inflow tubes and vacuum jacket, 

 in order to maintain the glass surface of the vacuum jacket 

 always at a constant temperature equal to the inflowing water. 

 The heat loss from the water is then the loss due to radiation 

 from the flow tube through the vacuum jacket, and conduction 

 from the ends of the flow tubes. 



In testing the accuracy of the method, the dependence of the 

 heat loss on the rise of temperature was found, and the depen- 

 dence of the heat loss on the flow. 



The results with different calorimeters and with different rises 

 of temperature are given in the following table : — 



Summary of the Specific Heat of Water from Smoothed Curve. 



The values of 8 represent the specific heat of water in terms 

 of a thermal unit equal to 4-2000 joules, which occurs at 9* C. 

 It is more suitable to select a thermal unit at a more convenient 

 part of the scale. The mean value of the mechanical equivalent 

 of heat from these measurements over the whole range is 

 4-18876 joules, which is very nearly equal to the value at 16° C, 

 which is 4-1883 joules. It seems desirable to select a unit at a 

 temperature which, if at the same time at a convenient part of 

 the scale, may be equal to the mean value over the whole scale. 

 The author has in consequence adopted a unit at 16° C, and 

 has expressed the specific heat of water in terms of this unit. 



Two formulje can be fitted very accurately over the scale. 

 Between 5° and 37-5° C, the following expression in terms of a 

 thermal unit at 16° is found to read, 



S =0-99733 + 0-0000035 (37 -5 - 0^ + o-ooooooio (37 -5 - /3). 



The same formula holds between 37 -5° and 55° by simply 

 considering all values of the cubical term positive. Above 55" 

 the simple formula 



S = 0-99850 + o-oooi 2o(/ - 55°) + o-oooooo25(/ - 55)-^ 

 holds with great accuracy. 



Physical Society, October 26. — Dr, Lodge, President, in 

 the chair, — The chairman read a letter from Prof. Cleveland 

 Abbe, of the United States Coast and Geodetic Survey, stating 

 tha.t the Monthly Weather Review would be sent regularly to 

 any member of the Physical Society expressing a wish to receive 



