14S 



THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



[May' 



The king post, straining collar (the horizontal heam) and struts from 

 side walls, 12ft. by 10ft. in two thicknesses and boiled together. The 

 purlins are 10 ft. by Gft. and about 9 ft. apart, being four in number on 

 each side of the span. The common rafters are 5 ft. by 2 in. and are 

 placed 3ft. apart from centre to centre. The ridge 12 in. by 2 in. 



By a comparison of the two roofs, the simplicity of the Newcastle 

 roof over that with curved ribs, is at once apparent ; no wall plates 

 are used at the foot of the struts on the side walls, and at the level of 

 the eaves ; a pole plate and vertical posts at the foot of eacli rafter is 

 dispensed with. The braces are prolonged to the king post, and act 

 both as a tie beam and a counter strut to the main struts or portion of 

 the curb roof, resting on the side walls at a level lower than the eaves. 

 The principle of this roof is that of the common curb roof, as by in- 

 spection of the sketch it will be seen that the strongest scantlings are 

 so arranged. On a few of the couples or pairs of principals a curved 

 rib is affixed to the tie beam and strut, so as to give the roof a curvi- 

 linear form; but as it is dispensed with in some, it shows that it is 

 not essential to the stability of the structure. 



I am, Sir, 



Si. Jinn's, Nemcasile-on-Tync. Your obedient servant, 



O. T. 



ON REVERSING LOCOMOTIVE ENGINES. 

 (With an Engraving, see Plate VI.) 



Sir — Having by chance fallen in with a number of your Journal, 

 (the number for February, 1842,) I perceive in it a design 

 for reversing locomotive engines, [signed H. and P., upon which, with 

 your permission, I beg to make a few remarks, as the principle of it 

 is similar to one of my own. 



In the latter part of the year lb42, I designed two plans for rever- 

 sing, the reversing valve being in the one case a slide, and in the 

 other a four way cock ; the former of these was published in a con- 

 temporary journal, > but having been forestalled in my design for the 

 latter, it was never published: the two grand objections to be con- 

 tended against in those designs, were, the pressure of the steam 

 against the under side of the slide when reversed, and the (as yet) 

 impossibility of obtaining double lead; to obviate the former of these, 

 I proposed the design enclosed, which is much more simple and less 

 complex than H. and P.'s plan. In the first place, the use of the four 

 way cock for changing the direction of the steam, does away with the 

 necessity of tilling up the smoke box with the piston valve, and is be- 

 sides, less expensive; secondly, the connexions between the pistons 

 in the icorkwg valve box, are mere rods, instead of the pipes used by 

 H. and P. ; thirdly, a loss quantity of steam pipes are required, as in- 

 stead of two sets of pipes between the reversing and working valves, 

 I use three short pipes crossing the bottom of the smoke box, con- 

 necting the centre of each box, and the aids individually. 



For explanation of my design, allow me to refer you to the sketches 

 enclosed. — See plate VI. 



A, is the steam pipe, which conveys the steam from the top of the 

 dome H, through the top of the smoke box, to the four way cock B, 

 from whence the pipes C and D, take it to the valve boxes, the pipe 

 C, connects the cock with the ends of each valve box, or that part on 

 the outside of the working pistons in it, and the pipe D, connects it 

 with the centres of each box or that part of the box let/can the pis- 

 tons, in Fig. 1 ; the four way cock (shown in section) is so set as to 

 allow the steam to proceed along the pipe D, to the centres of the 

 valve boxes, while the waste escapes up the pipe C, from the ends of 

 them, into the blast pipe ; there are three pipes between the valve 

 boxes E E, one of which is shown at F; the section of the valve box 

 in Fig. 2, shows the positions of these pipes, which enter the box at 

 K, K, K', the pipe D, being connected to the box opposite K', and 

 thence proceeding across to the other box, and the pipe C, being 

 connected opposite to the passages K K, and thence crossing to the 

 box on this side ; the mode of action of the valve is so simple, as not 



1 The Practical Mechanic and Engineer's Magazine. 



to require any explanation further than that the pressure is balanced 

 as effectually, as in H. and P.'s plan ; the dotted lines show the posi- 

 tion of the four way cock plug when reversed. Having, as I hope, 

 fully described by own plan, will you allow me to say a few words 

 respecting H. and P.'s mode of obtaining double lead, may I ask them 

 if this plan has ever been tried, and if so, if it was found to answer 

 the inventors' expectations, as it is my firm belief, that if it had been 

 tried before its appearance in your pages, it never would have made 

 that appearance. The mode of working two valves with one eccen- 

 tric, is an exceedingly ingenious one, and as far as I am aware, is 

 quite an original idea ; but it will not require much demonstration to 

 show the futility of the mode of obtaining lead, by the use of the 

 circular slots ; the mistake into which H. and P. seem to have fallen, 

 is by no means a solitary instance of premature conclusions, as witness 

 the propositions contained in the 3rd and 4th Vols. London Mechanic's 

 JWagazinc. I will take the same position of the eccentric, as given 

 by H. and P., thus in Fig. 3, let the perpendicular dotted line repre- 

 sent the position of the crank, being at half stroke, then (lead being 

 given) the position of the pin on the lever for working the valve, will 

 be at D ; but suppose thp steam passages to be reversed, the crank, 

 carrying with it the eccentric ring, will revolve in a contrary direction, 

 and the pin D, will not be moved until the crank arrives at C, as 

 shown in Fig. 4, consequently the valve will be just so much in arrear 

 as it had load in the former position, as the valve lever will not be in 

 the proper position for giving lead until the crank arrives at C, 

 whereas it ought to ho in the same position as in Fig. 3, which is at 

 half stroke. It is not, perhaps, generally understood, that the real 

 position of the valve to obtain lead requires no alteration, when re- 

 versed in this manner, but the relative position of the valve to the 

 motion of the eccentric must be altered. 



I am, yours, obediently, 

 42, Great Avenham Street, Preston, William Johnson. 



April 7, 1843. 



VELOCITY OF WATER DOWN VERTICAL PIPES. 



Sir — I have attentively perused the several articles which have 

 lately appeared in your scientific Journal, on the velocity of water 

 down vertical pipes under certain conditions; but I by no means agree 

 with your correspondent T. F. . . . n, who asserts, that the velocity of 

 water down a vertical pipe lb' feet long, under these conditions, will 

 be 32 feet per second. Nor does it appear to me, that the mutual 

 cohesion between the several layers or particles of water in the pipe, 

 is a force sufficient of itself, to account for the solidity of the issuing 

 stream, as stated in a late number of your Journal. — The following is 

 my humble opinion on this interesting subject. — 



First, as to the velocity of water down a vertical pipe 16 feet long 

 the top of the pipe being considered to be always covered with 

 water. — 



The following table extracted from " Grier's Mechanic's Dictionary," 

 exhibits the natural velocity due to a body, alter having fallen through 

 the undermentioned distances : and will be found useful as a reference 

 in the following remarks. — 



Space through Velocity acquired at Space through Velocity acquired at 

 which the body the eud of the time. which the body the end of the time. 



feet per second. 

 . 24704/ 

 . 25-9628 

 . 27-1232 

 . 28-2264 

 . 29-9786 

 . 30-3601 

 . 31-3176 

 . 32-2833 

 . 33-1975 



It appears from this table, which is founded on the well-known law, 

 that " the velocity acquired by a body falling from rest in a free space, 

 is as the square root of the space fallen through," that the velocity of 



