/S45.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



245 



enjoyed I'V (ho andiracites over tlie fureipn coals tried, wlietlier we 

 consider tliein under eqnal weiglils or equal Inilks. 



Experiment appears to demonstrate tliat, for tlie purposes of rapid 

 evaporation, and for tlie production of illuminating gas, the coal of 

 Indiana, though neither very heavy n'^r very durable, is inferior to none 

 of the highly liitutninous class to wllich it belongs; since in heating 

 power, anil in freedom from impurity, it surpasses the splint and can- 

 cel coal of Scotland. 



Ntctssity of /iirllier experiments. 



I cannot by any means regard the iiivesligalion of American coals 

 as an exhausted subject. 



A glance at any good geological map of the United States, in which 

 the coal fields are laid down, will show how exceedingly limited is 

 the whole amount of s;iace covered by the several detached coal 

 troughs from wliich the samples here presented wi're derived, com- 

 pared with the immense extent of that formation which covers western 

 Pennsylvania and Virginia, eastern Ohio, the eastern part of Ken- 

 tuckvj a part of middle Tennessee, and an undefined portion of Ala- 

 bama ; and much more when compared with the vast tr.icts of coal 

 country in Illinois, Iowa, Missouri, Arkansas, and a considerable por- 

 tion of Michigan. 



The surprising extension of steam navigation on the western rivers 

 and the north-western lakes, as well as on the gulf of Mexico and the 

 adjacent seas, the increase of population, and the consequent clearing 

 of woodlands, all point significantly to a necessity which must be fell, 

 at no distant day, to have recourse to mineral fuel for supplying this 

 rapidly increasing demand. 



To understand the relative strength and usefulness of the coals 

 from the several parts of the three great western coal regions, requires 

 that they be examined with no less care than has been applied to the 

 limited spaces from which were derived the materials operated on 

 during these experiments. It may he added, that the products of 

 many coal districts east of the Allegany mountains ire yet unexamined. 



If' in any case knowkdge be power, it is pre-eminently so when it 

 relates to a subject which constitutes the greatest element of power 

 in the physical world, and in the present age of marvellous develop- 

 ments. 



ON THE STKENGTH OF WOOD AND CAST IRON. 



Sir, — I had intended to lay before the Mechanical Section of the 

 British Association for the Advancement of Science, at tii*Mr late 

 meeting at Cambridge, a few remarks on some important points con- 

 nected with the Experimental Determinaliun of the Strength of Wood 

 and Cast Iron. The fewness of those who attended that Section ren- 

 dered it advisable to forego this intention; and in fact, by mistake, 

 my paper was described as "On the Strength of Iron Castings," which 

 was not my main object, but merely incidental to the other enquiry 

 "On the Strength ot Timber." However, though the meeting of the 

 Section was a failure, I of course met there with Mr. Eaton Hodgkin- 

 son, whose labours in the cause of science are so well known, and we 

 had some short conversation on the subject of Cast Iron. He iiiroruied 

 me that he had now preparing for publication a great mass of experi- 

 mental results which would contain results bearing on my views. As, 

 however, it may be some time before we are favoured with these 

 tab'es, and my object is to address the practical man rather than the 

 scientific, I will trouble you to notice the point 1 wished should be 

 attended to. It was suggested by Mr. Edward Bell, the Professor of 

 Machinery in our College, that by increasing the length of runner head 

 the strength of a horizontal bar niiglil be made equal to that of a ver- 

 tical bar, and would be much more uniform in its texture. He there- 

 fore prepared some bars for determining experimentally the advantage 

 — and found that it was as lie had apprehended. The reason of course 

 is obvious. The iron when in a fluid state obeys the laws of hydro- 

 statics, and tlie pressure increases with the dejith, and a very small 

 vertical column of iron, will produce a great pressure throughout the 

 liquid mass, a pressure proportional to its length. If, then, the column 

 is kept in a state of fusion while the metal in the fl isk is cooling and 

 setting, the particles will be packed more closely together, the density 

 will be increased, and a stronger bar obtained. In an economical view 

 this is very important, for a very inferior iron will by this means give 

 as strong a bar, or stronger, than a much belter, and therefore dearer, 

 iron. 



Experiments linve been m ide only on a small scale as yet, but we 

 purpose to extend them in number so as to generalise on the subject, 

 and ascertain whether, by a proper depth of runner head, we cannot 



make bars of a mixture of Garlsberrie II. and old fire-bars of the worst 

 scrap iron which shall be as strong as the best irons will give. 



1 liiid hoped that I shouU' have liul time to write a >liort account 

 of the researches we have made on the strength of limber, but I have 

 found it impossible for the present, — I will only draw your attention 

 to this point. In ascertaining the sireiiglh of timber, these two points 

 nuist be kept quite distinct, viz., the constant expressing the nlalive 

 III nnglh, and the constant to be used in the formula;, such as those 

 given in TiirnbuU, wliich we may call the constant representing the 

 absolute strength. 



If a hundred experiments are made on a particular kind of fir, the 

 lire, iking weight in each case being taken underexactly similar circum- 

 stances, the lUOtli part of the sum of all these weights represents 

 fairly enough the mean strength of that particular wood, (. t., it will 

 do to comfiare with a number determined in the same way for another 

 kind of fir, and the greater this tnean weight is, the stronger the wood. 

 So far, then, as scientific research is concerned, this method is fair, — 

 but the same constant will not do for the practical man. 1 say that for 

 this we must take the leant weight th.it broke the beam, and not the 

 mean, — for the workman wants to know not what the average strength 

 of the wood is, but how much he may trust to a particular specimen 

 of it; and therefore he wants to know what is the least weight that 

 broke a fair, uniform, sound beam under given circumstances. 



The first set of constants will guide him in the choice of his mate- 

 rial, but if he begins to calculate the dimensions from the formula, as 

 in Turnluill, he wants a dilTerent constant, viz., the one I have above 

 pointed out. 



My attention was drawn to this subject by reading the following 

 passage in Professor Barlow's book on Strength of Materials, page 2li. 



Practical Rule. — Since the strength of direct cohesion must necessarily be 

 luoporlional to the number of fibres, or to the area of the section, it follows, 

 that the strength of any iron rod will be found by multiplying the number 

 of square inches in its section by the corresponding tabular number as giveu 

 above. 



This, however, gives the absolute strength, or rather the weight that would 

 destroy the bar ; and practical men assert that not more than one-fourth of 

 this ought to be employed. 1 have, however, left more' than three-fourths 

 of the whole weiglit hanging for twenty-four or forty-eight hours without 

 perceiving the least change in the state of the fibres, or any diminution of 

 their ultimate strength. 



It will be seen that Professor Barlow uses the expression "absolute 

 strength" in the way in which I have proposed to use "relative 

 s/rength." 



I say that if ho proposed the smallest weight instead of the mean, 

 the result would be one which practical men ought to trust. As to the 

 arbitrary " one-Courth," it only shows that we have not yet succeeded 

 in proving to practical men that we em do them any good, and Mr. 

 Barlow justly intimates that there is a great sacrifice of the powers of 

 the material in this very arbitrary reduction. 



I trust to ofTer some further remarks on this interesting subject, — as 

 well as be able to lay before your readers at a future time results of 

 experimental enquiries made by Mr. Ranger, our lecturer and profes- 

 sor of general construction. I hope we shall be able to |)oint out some 

 very important features in the case, to which as yet but little attention 

 seems to have been given. 



I remain, Sir, 



Your obedient servant. 



College, Putney, July, 18-45. M. CowiE, Principal. 



COMPARISON OF ENGLISH, FRENCH, AND BELGIAN RAILWAYS. 



T/ie Fares cliaryed, the Expenses and the Profits. 



(From the Journal des D e bats, July 14.— Traiisiatfd for this Journal.) 



While so many railways are in the course of consliuction, it is interesting 

 to know as exactly as possible every item of expcndiiure connected with 

 them. An able engineer, M. Jullien, under whose direction are the works 

 on the line from Paris to Lyons, has undertaken to give an idea of these ex- 

 penses. The reports of the railways of France and abroad supply liira wit 

 materials which he has admirably digested and arranged. 

 Average Cost of Railtcay per mile. 



The first thing that strikes us in M. Jullien's Memoire is the observation 

 that the average of 300,000 fr. per kilonittre (.£19,200 per mile), generally 

 admitted as the probable cost of construction of the main lines in France, i»- 

 certainly loo small. Of this M. Jullien has j;ivcn proofs. This is an impor- 

 tant consideration at a time bke the prcieut, when iipeculatiua is so euijerly 



