1841.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL 



219 



into complete oblivion, and during almost the whole of the middle 

 ages this avt was wlioUy limited to casting bells. 



I:; Modern Times. 



At the Revival appeared several bronze works of art, in which 

 Italian artists, and particularly those of the famous school of Florence, 

 In the beginning of the lljth century, distinguished themselves most,- 

 and contributed most etiicaciously in ditfusing a taste for it in difierent 

 European countries. The sculptor Torrigiani ));\ssed several years in 

 England, where Henrv VIII. gave him several commissions for bronze 

 works. I'rimaticcio also executed, at Fontainebleau, several bronze 

 .statues from antique models which he liad hruuglit from Uome. At 

 this time there were several French artists who were employed in 

 brass founding ; but their modes of proceeding seem to have been very 

 imperfect, for Benvenuto Cellino relates in liis memoirs that during 

 bis stav in France, he vi-ished to cast a bronze statue of Jupiter about 

 six feet high, which had been ordered of him by Francis I. ; "but never 

 having been engaged in this kind of work," said he, '• I consulted 

 some of the old masters of Paris, and explained to them how we 

 managed in Italy. They replied that their manner was dilferent, and 

 that if I would leave it to them, they were sure to make my model in 

 bronze such as it was in clay. I made my bargain with them ; 1 pro- 

 mised them the price tliey asked, and even something over. I put 

 my hand to work, but 1 could see well enough that they were not try- 

 ing the right way. I wanted also to try myself upon a head of Julius 

 Csesar, larger than life, made after the model of a small head designed 

 from a beautiful antique which I had brought from Rome. I added 

 to it a head of the same size which I modelled from that of a beautiful 

 girl in my service, and whom I called Fontainebleau, from the name 

 of His Majesty's favourite palace. When I saw my furnaces finished, 

 and our models baked, I said to my master founders, I fear that the 

 Jupiter will not come out well, because you have not left draught 

 enough for the air ; but they replied that, if tliey did not succeed, 

 they would give me my money back again, and that I should tind less 

 chance of success in the Italian method. This took place before some 

 gentlemen whom the king often sent to see how I was getting on. 

 Before casting the melted metal for the Jupiter, the founders wanted 

 also to place my two heads to cast them at the same time, feeling 

 persuaded that their mode would not succeed, and that it would be a 

 pity to lose such 6ne works; but the king, who learnt it, sent to them 

 to tell them that they must think of learning from their master, and 

 not of teaching him. Then, smiling, they put their Jupiter in the pit, 

 and I also arranged my two heads at the sides, and when the metal 

 was ready, we left a free passage for it. Our moulds were quite 

 filled, and we were all happy, I, with having succeeded in my way, 

 and they in theirs. They asked me for something to drink, and I 

 gave them plenty of refreshments ; they then asked me to pay the 

 sum I had promised them. You smile, said I to them, then, but I 

 very much fear that you will cry soon; for I saw that more metal ran 

 into the Jupiter than was wanted, and that is the reason that I shall 

 not pay you until it is all right. These poor men felt that I was in the 

 right, and went away without saying anytliing. They returned the 

 next day very quietly to empty their pit, and began with the two 

 heads, which were perfect; they then came to the Jupiter, which 

 caused them to cry out, as I thought, for joy, and which made me run, 

 but I found their faces like those of the soldiers who watched the. 

 tomb of Christ. You see, said I, what has happened to you from not 

 believing me ; you would have reaped more profit and I more honour. 

 Learn, then, to work, and not to laugh at what is said to you. They 

 acknowledged their error, but they regretted their time and expenses, 

 on account of their families, whom tliey had to keep, and for which 

 they should be obliged to run into debt. Never mind that, said i, I 

 ■will' pay you as soon as the treasurer pays me ; for I pitied them, be- 

 cause they had worked with a good heart." Further on, telling the 

 story about his statue of Perseus, which was also cast in bronze, he 

 says, " The model of the Medusa, made of clay, and well-secured with 

 iron, had already passed through the fire; I had already covered it 

 with was, and the bronze only was wanting. I had my furnace built 

 directly ; I took such good care, and the figure came out so clean, that 

 my friends thought it was all done, like the French and German 

 founders, who never finish their bronzes after they come out of the fire, 

 being doubtless ignorant of the practice of the ancients, and many of 

 the moderns, who finish off with a hammer and chisel." This remark 

 of Benvenuto would lead us into the belief that the French and Ger- 

 man bronzes contained a good deal of tin ; for when the bronze con- 

 tains a good deal of copper, its fusion requires a very high tempe- 

 rature, which vitrifies part of the sand of the mould, which, becoming 

 attached to the figure in cooling, requires to be removed; on tlie other 

 band, a larger proportion of tin making the metal more fusible, this 



result was less to be feared. Benvpuuto, not contented with having 

 executed so many admirable works, left also a treatise on casting in 

 bronze, which was long the best manual on the subject. 



(To be contiimed.) 



ON THE POWER OF THE SCREW. 



SiK — There is an article by Mr. Cussen on the above subject in your 

 number for May, on which allow me to make the following remarks. 



His first objection to Mr. ijridge's formula seems to arise from a 

 want of acquaintance with the .»tyle of mechanical language. Surelv 

 Mr. H. just meant by d, the pitcli, or distance between the centres of 

 the threads, or, in general, the distance between the threads, just as 

 we talk of the length of an engine beam, when we mean its length be- 

 tween the end centres. Why did we not get an example from Bridges, 

 to test his meaning of the ambiguous rf? 



As to his second objection, he denies that the diameter of the cylin- 

 der is of no importance. One of 12 inches diameter, he says, will sustain 

 six times tlie weight with the same power t!iat one uf 2 inches will 

 do. Now this is not the point at issue. We are not talking about 

 mere pressure, but of moving power. Let him consider that when the 

 machine is set io motion, the velocity of the weight up tlie inclined 

 plane increases as the diameter of the cylinder. Thus his advantage 

 is neutralized by necessitating a greater velocity. But again, it is 

 evident that with the same power at the same leverage, whatever he 

 the diameter of cylinder, the weight that can be raised through the 

 same height in one revolution must be the same. It is an established law 

 that the momenta of power and weight are equal; therefore the mo- 

 mentum of the power, (viz. the product of its intensity by its velocity) 

 Being constant, that of the weight must also be constant ; 1. 1. since the 

 velocity of the weight is constant, (as it is raised througli the same 

 height each revolution,) therefore the intensity of the weight also is 

 constant, and this inference is quite independent of the size of cylin- 

 der. 



His third objection demonstrates that he has not thought three times 

 on what he says. He confounds the moment of power with its mome7i- 

 turn; a vital error. The moment of power is its intensity into its 

 leverage, but its momentum is its intensity into its velocity. Now 

 the relative velocities of the power and weight are the spaces ])assed 

 through by each in one revolution ; therefore the velocity of the latter 

 is the pitch of the screw, and that of the former just the circumference 

 of the circle described by its leverage. Therefore this element is 

 chosen correctly in Bridge's formula. 



ON LONG AND SHORT CONNECTING RODS. 



Observing that there exists a controve(Vsy respecting long and short 

 connecting rods, allow me to present the following demonstration of 



Fig. 1. Fig. 2. 



the justness of the action of all connecting rods, long or sliort. 



Let /re fig. 1, be the crank endof a side lever of a marine engine, eb 

 the connecting rod, and ab the crank moving as per arrow in the circle 

 6 /. The resistance at 6 acts always in the line of the connecting rod ; 

 let ec represent it in direction and intensity, just when the slightest 

 overplus of power would set the engine in motion. The power acts 

 always in the liae §• erf perpendicular to ke; complete the parallel- 



