350 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[September, 



leakage was 33 per cent., and in the other 25 per cent. Ileuce, I was in- 

 duced to conclude that the loss of power, whether caused by friction in the 

 one case, or by leakage in the other, is as nearly as possible the same in both. 

 We arc now come to the third subject of enquiiy, namely, the working 

 e.xpenses, wear and tear, &e. On our inclined planes, we have seven miles 

 of chain in work, weighing 70 tons, whicli last on an average, four years, and 

 cost about .^18 per ton; 70 tons at ;£18 per ton, amounts to £1260, £ s.d. 

 which divided by 4 gives an annual expense for chains, of . . 315 

 We have also about 1500 puUies, or rollers, which weigh J cwt. 

 each, cost £10 per ton, and last about seven years. Hence 1500 

 rollers at J cwt. each, weigh 56 tons, which at £10 per ton, amounts 

 to £560, and divided by 7, gives an annual expense of .... 80 



Axles, wood bearings, &c 10 



Sundries, such as large wheels, chain wheel, segments, preventers, 



tackling chains, shackles, coal, tools, damage, &c., 100 



Wages, estimated at 100 



£605 



la ascertaining the working expenses of the Atmospheric Railway, I was 

 assured by the gentleman who superintends it, that the amount was so tri- 

 fling that it might almost be left entirely out of the calculation ; indeed from 

 the remarks already made with regard to the wear and tear it will be inferred 

 that it cannot be large. The patentees allow in their £50 annually per mile, 

 for the renewal of the travelling apparatus. If, therefore, we take this sum 

 and £20 additional for piston leathers, grease, and sundries, we shall pro- 

 bably have the annual cost sufHciently near for our purpose. £75 per 

 annum therefore on 31 miles, will amount to £262 lOs., which, exclusive of 

 the interest on the permanent outlay, shews an annual saving on the Atmos- 

 pheric system of upwards of one half. 



I have purposely left out of the calculation everything relating to wages ; 

 because, not only the same description, but also the same number of men 

 would be employed in one case as the other. Proceeding with our enquiry, 

 our next object is to ascertain the amount of permanent outlay which 

 would be required in changing from one system to the other. Our 

 inclined planes are nine in number, and together are Sj miles in length. 

 Their inclinations vary from 1 in 6 to 1 in 16; hence, the Atmospheric 

 mains necessary to enable us to draw the same weights, as we now do, must 

 in one case be 27 inches, and in the other 17 inches diameter. The air 

 pumps being proportionate to the power of the engines, would for the 

 greatest be 44 inches, and for the least (leaving out the small engine at 

 Whaley), 32 inches diameter. The estimates of the patentees shew that a 

 main of 15 inches diameter, laid down and ready for use, would cost £3,350 

 per mile, and with the air pump £3,600. But much of the cost depends on 

 the weight of material ; and, as ours would require to be at least one half 

 heavier, in consequence of their increased size, we could not safely estimate 

 the cost at less than £5,000 per mile, which for 3i miles would amount to 

 £17,500. The interest on this sum at 5 per cent., would be £875 per annum, 

 and added to the working expenses, wear and tear, &c. amounting to £262, 

 would give the annual cost of the new system to us, at £1137 instead of 

 £600 as on the present plan. 



It is clear therefore that whatever might ultimately be gained, nothing 

 could be saved by the change ; while for any uncertain advantage which 

 might he expected to result from it, we should have a certain increased ex- 

 penditure to the extent of at least £500 a year. 



It now only remains that we should compare the advantages and disad- 

 vantages of the two systems ; and, with this view we have to enquire, in 

 what other respect the introduction of the atmospheric principle would be 

 beneficial. 



The only object of importance which we should gain by the change, would 

 be safety ; and although I am well aware of the value of perfect security, in 

 working inclined planes, I am nevertheless of opinion, that for a mere mer- 

 chandise traffic, the outlay of eighteen or twenty thousand pounds is consi- 

 derably more than the object is worth ; besides, so far as relates to the safety 

 of goods, we are now nearly as free from accidents, and damage arising there- 

 from, as we should be under any system. 



If to this we add that under the atmospheric system we should be subject 

 to inconveniences which we do not now experience ; it will tend further to 

 shew, that for a merchandise traffic, we are best as we are. The inconve- 

 niencies alluded to would arise in this way ; whenever a train of four or more 

 waggons arrive at our inclined planes, they are, if loaded, drawn up in pairs, 

 and as soon as one pair has reached the top, the other is immediately hung 

 on at the bottom and drawn up without any further loss of time ; but on the 

 atmospheric system, the train would be obliged to wait until the engine had 

 exhausted the main, unless it had been prepared in readiness; and, when the 

 first waggon had been drawn up, the next would not only have to wait until 

 the main had been re-exhausted, but also as much longer as would be re- 

 quired for the descent of the travelling apparatus ; making together, not less 

 than six minutes delay between each pair of waggons, in addition to the 

 time occupied in their ascent. The same kind of delay would occur to the 

 descending waggons, with this additional disadvantage, that in order to raise 

 the travelling apparatus between the descent of each pan: of waggons, the 

 engine must be kept in constant work ; the same for downward as for up- 

 ward traffic ; causing thereby, a considerable extra expense for coal and other 

 requisites. 



There are a few other inconveiueaces -which would result from the cbange, 



but those which 1 have already pointed out, being of the greatest importance, 

 and also quite sufficient to shew that the application of the principle to our 

 inclined planes, is by no means desirable, it is needless now to mention 

 them. 



From the preceding remarks it will, I think, appear evident, that the ap- 

 plication of the atmospheric principle to our railway in its present state, so 

 far from being any advantage, would, in fact, subject us not only to serious 

 inconvenience, but to considerable additional expense, and that too, (so far 

 as relates to our present traffic,) without any compensating benefit. It, how- 

 ever, by no means follows, that the principle cannot, under any circumstances, 

 be applied with advantage ; on the contrary, I am of opinion that it is pecu- 

 liarly applicable to the circumstances of our railway, if properly carried out. 



I am. Gentlemen, 



Your very obedient Servant, 



Raihoay Office, Cromford, John Leonard. 



July 1st. 1844. 



METHODS OF PAINTING ADAPTED TO MURAL DECORATION. 



By 0. L. Eastlake, Esq., Secretary to the Royal Commission on the 

 Fine Arts. 



Four modes of painting adapted for walls have been employed in ancient 

 and modern times: Tempera, Encaustic, Fresco, and Oil-painting. The three 

 tirst were known to the ancients ; the fourth method, invented by the mo- 

 derns and originally applied to moveable works, has been also employed in 

 mural decoration. 



Tempera is so commonly practised that it can hardly be necessary to enter 

 into a minute description of its process. It has, however, an interest from 

 its antiquity, and from its having been more generally in use in Italy than 

 any other method, immediately before the introduction of oil-painting. This 

 circumstance and certain difficulties in its practice appear, in some cases, to 

 have led to a union of the two methods. Tempera is applicable to the sur- 

 face of smooth dry stucco or to any similar levigated ground which lias either 

 been incorporated or covered with a due proportion of size or glue. It docs 

 not, like fresco, necessarily require to be executed at once, and admits of the 

 use of all colours which are not prejudicial to each other. White lead is 

 however excluded, because being unprotected in tempera from the action of 

 certain gases, it soon loses its brightness. The white used is principally 

 gesso marcio,^ to which white earths arc sometimes added. The binding 

 vehicle may be formed of animal glutens, such as size, yolk of egg," &c., or 

 of viscous fluids aud gums procured from the vegetable world, such as the 

 milky juice of certain trees and plants, solutions of gum arable, gum traga- 

 canth, &c.^ 



The practice of tempera-painting may be said to be carried to perfection 

 in modern scene-painting, in which imitation is chiefly confined to large 

 effects. But in this application of the art the difficulty of blending tints to 

 the extent required in figure-painting, so as to equal the completeness and 

 finish of oil-painting, is not encountered. The thinness of the vehicle and 

 the almost immediate change of the tints in passing from the wet to the dry 

 state renders a certain abruptness of execution unavoidable. This peculiarity 

 is compatible with great truth of imitation when the work is seen at a suffi- 

 cient distance, and the crispness of execution which is the result, is, with the 

 moderns, the characteristic of tempera. 



The early Italian masters, when they painted altar-pieces in this method 

 on cloth, endeavoured to attain the requisite finish by continually damping 

 the back of the painting.' This enabled them to complete a given portion 

 while in the wet state, and to give it any degree of softness that was desired. 

 But this was only applicable to pictures executed on a thin and porous sub- 

 stance ; tempera pictures on wood or on walls, in which finish is aimed at, 

 cannot be so treated, without some modification of the vehicle or by con- 

 tinually moistening the surface in front. Some of the early Florentines and 

 painters of the neighbouring schools adopted a more laborious method, but 

 less satisfactory in its result."' They attained the completeness they sought 

 by minute hatchings. A tempera picture in the National Gallery, attributed 

 to Perugino, is a specimen of this laboured process. 



The varieties of practice in the early examples of tempera, are also partly 

 to be attributed to the varieties of the vehicle. The Greek illuminations in 

 MSS. immediately preceding the 13th century, are generally painted in tem- 

 pera with a very thick vehicle, and this system was adopted by the Italians, 

 even for paintings of a much larger size, up to the time of Giotto. He ap- 

 pears to have been the first to introduce a thinner medium. In his works, 

 while the tints are blended, the minute handling, which is almost unavoidable 

 with the older practice, is not apparent. The thinner vehicle was composed 

 of yolk of egg diluted with water, and combined with the milky juice of 



1 Plaster of Paris stirred with much water till it loses the power of * setting.' In the 

 early Florentine descriptions of the process of tempera, white lead is mentioned ; this is a 

 proof that paintings so executed must have been subsequently varnished, and accordingly 

 the early Italiau worlds in tempera are always found to have been so treated. See " Cen- 

 nini, Trattato," &c., p. 70. 



2 The Italian writers restrict the term tempera to the vehicle of yolk of egg more or 

 less diluted. The modern practice ifl to add, by degrees, a small wine-glass of white vine- 

 gar to a yolk well beaten. 



3 See "Armenini de Veri Lrecetti della Pittura." Kavenna, 1887, 1. 2, c. 8; and 

 *' Vaaari," Introduzione, c. 20-25. 



> See "Armenini," ib. " Vasari," ib, c, 26. 5 "Armenini,""'' 



