338 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[XovEMcnn, 



Hull, 36,000 



Kseler, 20,000 



Newcastle, 20.000 



Carii.-,lH, 20,000 



Chester, 10,000 



Dundee, 10,000 



Ipswich, 10.000 



111 consequence of new arrangements made by the companies, a 

 great increase of business has taken j)lace in the carriage of book- 

 sellers' parcels. Tliere is a great tendency in tlie parcels traffic to 

 increase in consequence of the extension of the supply of the 

 local grocers, linen-drapers, Ike. from London and the great towns, 

 for it is well known that instead of taking stock a few times yearly, 

 they now receive frequent supplies. 



The chief parcels traffic is on the following lines : — 



No. of Parcels. Receipts. 



London and North Western, 2,000 000 £104,738 



Great Western, 700,000 34,li35 



Midland, 600 000 2S,9Se 



Eastern Counties, 480,000 1C,GG9 



Lancashire and Yorkshire, 400,000 5,225 



York and North Midland, 300,000 13,470 



York and Newcastle, 300,(100 8,721 



London and South Western, 200,000 10,029 



London and Brighton, 200,000 9,590 



South Eastern, 200,000 8,793 



No. XXIII.— MAILS. 



The receipts for mails in each of the years ending June 30, is as 

 follows ; the amount for 1845 being made up by doubling the 

 return for the half-year ending June 30, 1845 :— 



* Halfye.T. 



The total receipt detailed in 1845 was £77,000, to which has to 

 be added for omissions £23,000, making a gross total of £100,000. 



The total receipt detailed in 1847 was £lOS,872, to which has to 

 be added for omissions £25,000, making a gross total of £130,000. 



THEORY OF STEAM-ENGINES. 



Account of flic experiments to determine the principal liivs raid 

 numerical data which enter into the calculation of Stcam-Enginee. 

 By M. V. Reonaii.t. 



( Continued from page 268.^ 



Fourth Memoir. — on the measurement op temperatures. 



We do not as yet possess any direct means of measuring the 

 quantities of heat absorbed by a body under given circumstances, 

 and we recognise this absorption of heat only by the changes which 

 occur in the state of the body, or by its dilatation. Tlie name 

 thermometer is given to the instrument whose object is to indicate 

 the variations in the quantities of heat in any medium. These 

 instruments are generally founded upon the dilatation wliich bodies 

 undergo by the action of heat, or upon the changes in elastic force 

 which the same bulk of a gas experiences under the circumstances 

 to which the medium is submitted. 



A perfect thermometer would be one whose indications were 

 always proportional to the quantity of heat which it had absorbed, 

 or, in other words, one in which the addition of equal quantities 

 of heat produced always equal dilatations. To fulfil this condition 

 it is necessary, either that the capacity for heat, and the dilatation 

 of the thermometric substance, should remain invariable during 

 the experiment, or that these two elements should vary strictly in- 

 versely as each other. 



Nor would the perfect thermometer yet indicate the quantity of 

 heat absorbed by the medium under given circumstances, unless 

 this medium presented the same advantages as the thermometric 

 substance — that is, unless it absorbed equal quantities of lieat for 

 equal variations of temperature as noted by the thermometer. 



But a comparative study of the dilatations of different sub- 

 stances under the same circumstances, quickly shows that they are 

 far from following the same law; and if we compare together the 

 quantities of heat absorbed by these different bodies when brought 

 successively to different temperatures, measured by the dilatations 

 of one of them, we see that these quantities are variable, and un- 

 equally variable in each one of them, without our having been 

 able heretofore to show the relations which exist between these 

 variations of capacity and the changes of bulk. 



The great precision which can be obtained in the construction of 

 the mercurial thermometer, the facility with which the thermo- 

 metric liquid may be obtained of the same degree of purity, and 

 the great extent of temperature through which this liquid pre- 

 serves the same state, have gi\en to the mercurial thermometer 

 the preference over aU other instruments of the same kind, and 

 have caused its adoption almost exclusively for all precise experi- 

 ments. 



But there is an essential condition which every apparatus for 

 measurement ought to satisfy ; it is, that it should not only 

 remain rigorously comparable with itself — that is, that it should 

 always mark the same degree under the same circumstances, — but it 

 is moreover necessary that we should be able to reproduce it at 

 will, and obtain always instruments rigorously comparable. 



Physical philosophers have thought that they had completely 

 attained this end, by making the scales of the mercurial thermo- 

 meters agree at certain normal temperatures which are easily re- 

 produced and always perfectly identical ; for this purpose, they 

 have adopted the constant temperature at which ice melts, and 

 that not less ponstant which saturated steam presents when it 

 exerts an elastic force of 70 millimetres. But I have shown 

 (Annates de Chimie et de Physique, 3rd Sirie, tome y., pages 100 et 

 seq.,J that two mercurial thermometers, adjusted for the same fixed 

 points of melting ice and boiling water under a pressure of 76 

 mm., may show very considerable differences in their movements 

 beyond these fixed points, if they are not made of glass of the 

 same nature. Even when the glasses of the reservoirs present the 

 same chemical composition, there may still be very sensible differ- 

 ences in their indications according to the way in which the re- 

 servoirs have been worked in the glass-blower's lamp, the molecular 

 state of the glass undergoing very notable alteratious during this 

 working. 



The mercurial thermometer, then, as it has been constructed up 

 to the present time, is defective in one of the most essential con- 

 ditions which ought to be required of an apparatus for measure- 

 ment — it cannot be always rejiroduced in the same state ; and the 

 .different instruments of the same kind are rarely comparable with 

 each other beyond the fixed points of their scales. 



Physical philosophers thought that they had observed that all 

 the gases dilate exactly the same fraction of their volume at 0°, when 



