1840.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



.3Se 



the boats. When a boat is required to pass from a higher to a lower level, 

 the how end, which must be armed with an inclined ]n-ojeetion, depresses the 

 gate as much as the depth of the immersion of the boat, and as much water 

 escapes as can jjass between its sides and the walls of the contracted part of 

 the basin. The same action takes place in ascending, except that a certain 

 amount of jiower must be expended to enable the boat to surmount the dif- 

 ference of level betv\een the basins. The quantity of water wasted by each 

 boat would be in proportion to its immersion and the speed at which it passed 

 over the gate. In case of diflerent sized boats passing along the same canal, 

 it is proposed to ha%e a small gate forming pait of the main gate, so as to 

 avoid the loss of water which would ensue from the whole width being open 

 for the passage of a small boat. 



This system has only been tried by models ; but it is proposed to make an 

 essay on an extensive canal next summer, when the results will be communi- 

 cated to the Institution. 



May 5. — The President in the Chair. 



The following were balloted for and elected : — Angier JTarch Perkins, St- 

 George Burke, and Beriah Botfield, as Associates. 



" Description of the Enginen on board the Iron Steam Tug, the Alice^ By 

 J. Patrick, Inst. C. E. 



The speed of this boat having far exceeded the constructor's expectations, 

 induced the author to send a description of her proportions, and of the con- 

 struction of the engines. The chief peculiarity in the engines is their being 

 placed in the centre of the vessel, with the two cylinders in a line with the 

 keel, and placed at an angle of 45°, inclining inwards towards the paddle 

 shaft, to which the motion is communicated direct (without the use of side 

 beams) by long connecting rods attached to the cross heads, which are 

 placed at the lower ends of the cylinders, instead of being on the top as in 

 the usual manner ; the connecting rods are thus enabled to be three times 

 instead of twice the length of the stroke, as is usually the case. The framing 

 is entirely of wrougbt-iron on the tension principle, and appears to resist the 

 tendency to vibration better than cast-iron framing. For the two cylinders 

 of 31 inches diameter, there is only one air pump of 22i inches diameter, 

 with 19-J inches length of stroke, instead of the usual complement of two air 

 pumps, 18 inches diameter each; this is found to be sufficient, as a vacuum 

 of 13f lb. per square inch is maintained. One of the advantages proposed by 

 this mode of construction is the reduction of weight ; these engines only 

 weighing 9 cwt. per horse power. The small space occupied leaving more 

 room for passengers, they are particularly adapted for river navigation, where 

 the breadth of beam must be limited. The simplicity of their construction 

 renders them less liable to expensive repairs. 

 The principal proportions of the Alice are — 



Feet. Inches. 

 Length between perpendiculars ... 95 



Breadth of beam 20 



Draft of water ...... 4 6 



Diameter of wheel 14 



Size of engines ..... two 30 horse power 



Diameter of cylinder . . . . . 31 inches 



Length of stroke ...... 3 3 



The engines were constructed by Messrs. Davenport and Grindrod, of 

 Liverj)0ol. Drawings of the boat and engines accompany this communica- 

 tion. 



" Deseription of an Apparatus for preventing the Explosion of Steam 

 Boilers." By Robert M'Ewen. 



The frequent explosions of steam boilers, caused in many instances by the 

 steam being confined until it acquires a density greater than the boiler can 

 resist, induced the author to invent a simple, self-acting apparatus, intended 

 to warn the engineer whenever the pressure exceeded the proper degree of 

 safety. 



The apparatus under consideration is constructed on the principle that 

 steam, in proportion to its density, will support a column of water or mer- 

 cury, of a given height, and that any fluid will find the same level in two or 

 more vessels, provided there be a free communication between them. It may 

 be called a mercurial safety valve, and consists of a cyUnder, within w liicli 

 are two cups, with two pipes dipping into them of a length proportioned to 

 the pressiu-e of the steam ; these pipes are connected at the top with two 

 valves on one spindle, so arranged, as that when one is open the other must 

 be closed. On the top is a waste steam pipe open to the atmosphere. One pipe 

 being filled with mercury, and the valve connected with it being open, the 

 mercury remains stationary until the pressure of the steam exceeds its proper 

 point. It will then be blo-mi out and fall into the empty cup, allowing the 

 steam to escape by the waste pipe, and giving warning to the engineer by its 

 noise. When the pressure is again reduced to its proper point the valve is 

 reversed, and the mercury will, on the next occasion of an increase of pressure, 

 be blown back again, still giving warning on either side. 

 Plans and sections of this apparatus accompanied the paper. 

 " On setting out Railway Curves." By Charles Bourns, Assoc. Inst. C. E. 

 Mr. Bourns having been engaged in setting out the Taff Vale Railway 

 tlirough a country presenting circumstances of more than ordinary difficulty, 

 which rendered it necessary to vary the radii and the flexure of the cm-ves 

 frequently, his attention was particularly directed to the sulijeot ; and he has 

 treated it in this paper clearly and successfully, demonstrating the severaj 



cases geometrically, and generally in a plain and satisfactory mannei-. He 

 calls attention to the inaccuracy of applying a square to the setting out of 

 segmental curves, particularly those of short radii, and recommends an offset 

 staff as theoretically correct and practically much more convenient. The 

 general rule to find the offset is — " Divide the number of inches in the chain 

 used by the number of such chains in the radius of the required curve, the 

 quotient is the offset in inches." The paper is accompanied by a table of 

 offsets for curves of different radii ; which the author found extremely con- 

 venient for use in the field. 



The paper being altogether mathematical is not adapted for publication in 

 abstract ; but it will be given at length, with examples and diagrams, in the 

 Transactions of the Institution. 



" Description of an Instrument for describing the Profile of Roads." By 

 Heniy Carr, Grad. Inst. C. E. 



The object of the author was the construction of a machine, which, being 

 drawn along any road of moderately even surface, should describe the section 

 of the line over which it passed. It is evident, that if a pendulum be sus- 

 pended from a frame standing perpendicularly when the machine rests on a 

 horizontal plane, on passing over a plane inclined at any angle with the 

 horizon, the pendulum must form the same angle with the frame the tan- 

 gent of which angle in terms of the radius will be the rise or fall of the • 

 plane. The duration of the tangent will be determined by the paper on 

 which the secti.^n is drawn being made to traverse at a speed proportionate 

 to the distance passed over; and the extent, by the diflerence of the speeds 

 of a nut and screw which are made to revolve in the same direction — the nut 

 turning at a constant velocity, and the screw at a speed differing from that 

 of the nut in proportion to the tangent, slower or faster as the tangent is 

 plus or minus, raising or lowering the nut according to the deviation of the 

 plane from the horizontal line. 



The machinery is set in motion by the wheels of the carriage, and a series 

 of wheels and pinions of given diameters cause the ground line and datum 

 Une to be drawn simultaneously by two pencils on a paper which gradually 

 unfolds itself from one drum, and is transfered to another at the rate of 16 

 inches per mile passed over, or on a scale of 5 chains to the inch. A profile 

 of a line of country may thus be obtained with sufficient accuracy for a pre- 

 liminary survey. 



A comprehensive perspective drawing accompanies the paper, and explains 

 the construction of the machine. 



May 12. — The President in the Chair. 



" Photography, as applicable to Engineering." By Alexander Gordon, M. 

 Inst. C. E. 



The object of the author in this paper is to direct general attention to the 

 advantages which may be expected to result to the profession of the Ci«I 

 Engineer from the discoveries of Mans. Daguerre and others, in enabling 

 copies of drawings, or views of buildings, works, or even of machinery when 

 not in motion, to be taken with perfect accuracy in a very short space of 

 time and with comparatively small expense. This system of copying not 

 only the outline, but the tints of light and shade, united with accurate linear 

 perspective, he contends may be easily adapted to the purpose of the engi- 

 neer, as well as to all those professions in which the art of drawing is used. 

 The photographic apparatus has already been employed to bring before us 

 exact copies of the most interesting monuments of antiquity, the French 

 antiquarians and artists having found it more easy and correct to Daguerreo- 

 type the Egyptian monuments and decipher the hieroglyphics at their leisure, 

 than to labour over the originals. 



The subject is divided into two branches : the first being the art of copjing 

 drawings and plans by the transmission and absorption of light by prepared 

 paper. The drawing to be copied is placed between two pieces of plate glass, 

 held down in close contact with a sheet of photogenic paper, prepared by 

 being washed over on both sides with a neutral solution of nitrate of silver 

 of a spectfic gravity of 1'0G6, and afterwards with a solution of common salt 

 and water (lib. of salt to 25 pints of water). The paper thus prepared must 

 be dried and kept in the dark, on account of its peculiar delicacy. The rays 

 of the sun are then permitted fo pass through the white portions of the 

 drawing or print, while they are interrupted by the black hues, and more or 

 less by the tinted portions. The rays of light thus act upon the prepared 

 paper, and produce, in a few minutes, a reversed copy, reproducing the lights 

 of the oi'iginal in shadows ; this c;^ be remedied by taking a second copy 

 from the first, and thus the shadows are restored to their original positions. 

 To destroy the sensitiveness of the prepared paper, and preserve the copy, it 

 is soaked in pure water, which carries off the excess of nitrate of silver, then 

 covered with a solution of hjiio-sulphite of soda of a specific gravity of 1,055, 

 and again washed in pure water, so that when dried it is permanently fixed. 

 It is evident that a copy thus obtained must be exactly like the original, and 

 the value of such a process may be readily estimated by engineers. 



The second branch, which is named '• Daguerreotype," after the distin- 

 guished artist who brought it to its present state of perfection, is of a much 

 higher order. This is the art of fixing and preserving on the surface of a 

 poUshed silvered plate the images collected in the focal plane of a camera 

 obscura. 



The process is rather complicated, but may be thus briefly described. The 

 surface of the silvered plate being cleaned and polished very perfectly by 

 means of finely levigated pumice stone, olive oil, and cotton, is rubbed 

 lightly over with diluted nitric acid, in the, proportion of 1 pint of acid to 



