lSi7. 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



353 



If («— 1) w' = or exceed 2 w, it follows that the girder in scale u will 

 not be able to support any weight at its centre, without the tension and 

 thrust per square inch being increased. 



Ejcample. — A. model girder, length 80 feet, weight 10 tons, breaks with a 

 weight of 30 tons in the middle : what weight will break a similar girder 

 480 feet long ? 



V„. ^ (2"'-("-I) "-•)"= ^ («»-50)-^" = 180 tons. Ans. 

 2 2 



We have been especially induced to call our readers' attention to the sub- 

 ject of model experiments, from the fact that the proposed tubular bridge 

 over the Menai Straits is to be constructed, as to its dimensions, according 

 to laws developed in a series of experiments, conducted by Mr. Hodgkinson 

 at Blackwall. We much fear that the enormous width to be crossed with- 

 out a support will prove too much even for the known inijenuity of Mr. 

 Stephenson. If, however, the talents of that illustrious engineer should 

 prove equal to the magnitude of his conception, none will feel more satisfac- 

 tion than o\irselves at his success ; and with mingled wonder and pleasure 

 shall we witness — at a respectful distance — his aerial tunnel quivering and 

 bending beneath a load of '* moral agents," happily unconscious of the laws 

 of equilibrium and of the depth of the cold dark waters above which they 

 are being whirled. 



(To be continued.) 



REGISTER OF NEW PATENTS. 



NASMYTH'S PATENT SCREW COCKS. 



The accompanying engravings show an important improvement in sluice 

 cocks, as patented by Mr. Nasmyth, of the Bridgewater Foundry, near 

 Manchester. In consequence of the facility with which they are manu- 

 factured, the cost of them is considerabiy less thau that of the ordinary sluice 

 cocks, and at the same time they appear lo us far more effective; but ihe 

 following testimonials, coming as they do from geutlenien well known as 

 practical hydraulic engineers, will show the value of the cock far better 

 than anything we cau write. 



Fig. 2. 



Fig. I is a 

 the pipe ; fig 



w of one of th 

 of cover; fig. 



e cocks ; fi 

 4, a transv 



. 2, plan a 

 erse view ; 



hove 

 and 



the level of 

 fig. 5, asec- 



lioual elevalion of n cock fully open, — the dotted lines show the position 

 of the valve wheu closed. 



Fig- ■•. Fig, 5. 



Mr. Nasmyth claims as new— 1st. The valves being formed with double 

 faces ; 2ndly. The screw passing down through the valve ; and 3rdly. The 

 casting of the cock in one piece. 



(To Messrs. Nasmyth, Gaskell, and Co.) 

 Gentlemen, — I have great pleasure in complying with your request, to 

 give an opinion upon Rlr. Nasniylh's Screw Cock for Water Works.' I 

 have examined and proved two of the cocks, and am quite satisfied that they 

 will answer, in an eflicient manuer, all the purposes for which this kind of 

 Cock is intended. 



One important feature in your Cocks, as distinguished from those ordi- 

 narily used, is, that they are ail double-faced, and therefore, there is no 

 occasion to have two sets, one single-faced, and one double-faced, and the 

 cost is considerably less than that of the ordinary single-faced Cocks, 

 which are cheaper than the double-faced. 



Screw Cocks form no inconsiderable item in the first and annual expen- 

 diture of a Water Works, and not unfrequently a single-faced Cock is 

 introduced, on account of its cheapness, where a double-faced would 

 otherwise be preferable. 



A comparision between the cost of your Cocks, and of ordinary, single, 

 and double faced Cocks, in equal proportions, should be made in order to 

 show the superiority of yours in a commercial point of view, which, after 

 all, is the most important view to be taken in the introduction of improve- 

 ments. 

 The value of Seven single faced Cocks, of the ordinary i 

 constructions, and of the following sizes, viz. — 3, 4, 5, J 

 6, 7, 8, and 9 inches, v\'ill be . . . . ) 



The value of the same number, and of the same sizes, of ) 

 double-faced Cocks, of the ordinary construction, will v 

 be ......... ^ 



The mean cost of the two classes 



The cost of the same number and of the same sizes of 

 your improved (Jocks, which are all double-faced 

 therefore will answer the purpose of single or double 

 faced, will be .... . 



Difference in favour of your Cocks . 

 Thus it appears that your Cocks are 30 per cent, cheaper than the ordi- 

 nary Screw Cocks, and equally efficient. 1 have therefore great pleasure 

 in recommending their use. 



I understand, that if a contract is entered into by you, for the supply of 

 these Cocks, that you undertake lo guarantee them for twelve mouths alter 

 they have been placed in the ground, and to take upon yourselves the 

 responsibility of all costs and charges which may be incurred should any 

 of them prove defective during that period, and further, that your prices 



46 



£43 18 



;s of^ 

 , and f 

 Jble r 



48 13 



40 



31 15 



14 10 9 



