1S41.J 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



2S1 



Watt's invention, what lie would have required to add if he had lived 

 to witness its present extended use, its multifarious applications, its 

 varied forms, its modifications in material and construction* He has 

 endeavoured to place before the reader, in a simple form, all the most 

 important information which many yeais of research and of practical 

 experience in a favourite subject have placed in his possession ; and 

 " the reader who is familiar with the subject will," he says, " readily 

 discover that he has read and thought for himself, and that his errois, 

 if manv, are at least his own. In one point he trusts he has facilitated 

 the progress of the student. While giving the general reasoning of 

 complex calculations, he has endeavoured to disembarrass them as 

 much as possible of that parade of calculus which exhibits the author 

 at the expense of the reader; and rather to present their results in 

 that simple form in which alone great truths present themselves to 

 those who thoroughly understand them." 



The plan of the work here laid down is in accordance with the 

 nature of an Encyclopjedia, wliich, being a work of a popular charac- 

 ter, and a book of reference rather than instruction, many, if not the 

 majority of its readers, moreover, being uninitiated in the arcana of 

 abstruse matliematical science, and therefore willing to take for 

 granted the truth of propositions, the demonstration of which they 

 are unable to comprehend, sliould not be unnecessarily encumbered 

 with complex and difficult calculations. It should, however, at the 

 same time be borne in mind that some, and we trust we may say many, 

 of the readers of the Encyclopaedia are possessed of snIBcient scien- 

 tific knowledge to enable them to think and judge for themselves. 

 Therefore, although the facts advanced should in general be such as 

 are recognized by the best acknowledged authorities, and in support 

 of which it suffices in most cases to cite the authority, yet, when any 

 new proposition is etmnciated, or any new doctrine propounded, it 

 should be accompanied by a rigorous demonstration, or it must incur 

 the risk of being rejected as unfounded. There are two instances in 

 the work under review, in which we do not find the reasoning ade- 

 quate to justify the conclusion ; we allude to the determination of the 

 best vacuum in the condenser of a steam engine, page 27(j, and of the 

 best proportion of poner to tonnage in sea-going vessels, page 'JSS. 

 We must, however, remark, in justice to the author, that we have 

 seldom, if ever, met with a work so full of typographical errors, by 

 which so much unnecessary labour is imposed on the reader, that many 

 are deterred from attempting to make themselves masters of the 

 author's meaning, and which are in some cases so serious as perhaps 

 even to render the accomplishment of the task impossible. Some of 

 the errors are of such a nature that it is difficult to decide whether 

 they are to be ascribed to the author or to the printer. 



The article Steam, which occupies nearly the first half of the 

 volume is on the whole a valuable contribution, particularly the second 

 section, in which are collected together all the most recent experi- 

 mental researches concerning the elastic force of steam at different 

 temperatures, as well as the most esteemed of the earlier experiments, 

 accompanied by figures of the apparatus employed. 



In the first section, where the projierties, phenomena, and appli- 

 cation of steam are considered in a general manner, there is the fol- 

 lowing simple illustration of the doctrine of latent heat by Dr. Dalton, 

 from which those who are not familiar with the operations of heat 

 may form a tolerably correct notion of the phenomenon in question: 



The liquid and its vapour may be con- 

 sidered as two reservoirs of caloric, capable 

 of holding different quantities of that fluid. 

 Let figure 1 represent to us such an arrange- 

 ment ; the internal cylinder of smaller capa- 

 city, the external one of enlarged capacity 

 surrounding and extending far above it, and 

 a small open tube of glass, communicating 

 freely at the bottom with the internal cylin- 

 der. Let us now conceive water to be poured 

 into the internal cyUnder, the water will mani- 

 festly flow into the slender tube tdl it stand 

 on the same level in the tube as in the cylin- 

 der. If any additional quantity be now poured 

 into the internal cylinder, the rise of water 

 in the slender glass tube will serve as an in- 

 dex of the quantity of added fluid ; and when 

 it is filled to the top, the fluid will stand at 

 the height marked 212", and will still be a 

 correct index of the addition of fluid. But if 

 more water be now adiled to it, it will not 

 make its appearance in the slender tube, but 

 will simply overflow from the internal cvlinder 



* The article on the Steam-engine is, ue belie\e, published in a st.p;ir:ite 

 volume ; bm, as we have not yet seen it, we are unable to notice it in this 

 monih's Journal. — Ep. C. E. Si A. Jodbnal. 



over into that of enlarged capacity, so that, while a large quantity is passing 

 into the vessel and gradually filling it up to 212', no ad.litional rise takes 

 place until the whole of the outer cylinder becomes filled to that point, after 

 which any further addition will again become sensible, by a corresponding rise 

 in the tube. This process is in precise analogy to the succession of circum- 

 stances in lieating a liquid, and converting it into steam. The internal cyhn- 

 der represents the liquid, the external one the vapour of greater capacity, and 

 the slender glass tube at the side the thermometer placed in communic ition 

 with tliem. When heat flows into the liquid, it passes equally into the ther- 

 mometer; and each increment of the one produces an equal increment in the 

 other, until the liquid reaches the limit of its capacity, when it suddenly be- 

 gins to enlarge its bulk and take the form of steam ; but the quantity of heat 

 required to fill up this enlarged capacity is so great, as to require about 5i 

 times as much to fill it as was contained in the whole liquid before, so that 

 all this time the thermometer is standing still, and it is not until the whole 

 of the steam is thus supplied with 212' of caloric, that the thermometer will 

 begin to show any further elevation; after which, any increment of heat 

 thrown into the steam wUl make its appearance on the thermometer, and 

 proceed as formerly, by simultaneous increments. 



As a practical application of the influence of pressure on the boiling 

 point of water, the following rule is given for finding the heights of 

 mountains by boiling water : 



Boil pure water in an open vessel at the bottom of the elevation, and ob- 

 serve on the thermometer the point at which it boils. Boil it again at the 

 top of the mou!itain, and observe with the thermometer the point at which 

 it now boils : the difference of temperature, multiplied by 530 feet, will give 

 a close approximation to the height of the upper above the lower station. 



This will give an approximation ; but, if greater accuracy be required, it 

 will further be necessary to correct for the difference of the temperature of 

 the air at the two stations, in the following manner. Add the temperatures 

 of the air at the stations, and subtract 64 from their sum, nudtiply the re- 

 mainder by one thousandth part of the height found; and this will be the 

 correction to be added to the height formerly found. The result thus found 

 will stdl require a slight correction for the figure of the earth and latitude of 

 the place ; but this does not amount to more in our latitude than an addition 

 of about two feet in a thousand, which forms a second correction. 



To iUustrate the mode of deducing heights from the boding point, as we 

 have given it, we take tlie following example. 



Water boils on the top of Bei: Nevis at 203-8°, while at the side of the 

 Caledonian Canal it boils at 212*, the temperature being 30° on the summit 

 of the mountain, and 35" below. In order to determine the height, 

 From 212° 



Take 2038° To 30° 

 Add 35° 



There remains 8-2° 

 Mioltiply by 530 



2460 

 410 



Sum 



Subt. 



65° 



64° 



4346 first approx. 

 4 first correct. 



4350 second approx. 

 8-7 second correct. 



Remain 1° mult, by 4-316 



Latitude 56° nearly 

 Mult. 4-350 

 by 2- 



8-700 



Calc. height, 43587 third approximation. 

 4358- true measured height — the difference being less than 1 foot. 



This method, however, is seldom susceptible of so high a degree of accuracy, 

 even with the most carefully conducted experiments. 



There is also a description with explanatory figures, of the elegant 

 and compact apparatus contrived by the Rev. F. J. H. WoUaston for 

 facilitating the procedure of taking the observations with the requi- 

 site precision. 



Among the contents of the second section we may mention, as par- 

 ticularly worthy of notice, the abridged account of the experiments 

 undertaken bv the French Academy of Sciences, and conducted prin- 

 cipally by the M. M. Arago and Dulong, having for its object the dis- 

 covery of the relation existing between the temperature and elastic 

 force of steam ; and those conducted, with the same object, by the 

 committee of the Franklin Institute of Pennsylvania, appointed to 

 examine into the causes of the explosions of the boilers used on board 

 of steam-boats, and to devise the most effectual means of preventing 

 the accidents, or of diminishing the extent of their injurious effects. 

 The former were completed in 1829, and are in every respect entitled 

 to a larger share of confidence than the latter, as well on accoimt of 

 the greater perfection of the apparatus employed and the extraordi- 

 nary care bestowed upon the manipulations, as the names of two phi- 

 losophers so well versed in experiments of a similar nature. 



In the 3rd section, ort the mathematical law which connects the elastic 

 force of vapour with its temperature, Mr. Russel has certainly laid 

 before his readers a considerable collection of fori^nlse (15 in nimber) 



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