1S41.] 



THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



23 



variations above or below the datum line. These memoranda are made upon 

 a strip of paper, which is fastened pu a table, along whirh an inde\ travels at 

 a velocity conesponding with that of the paper on the cylinder ; so that the 

 strip of paper being afterwards laid upon the section, the points marked may 

 be squared down \iithout using the scales. 



"When the distance of live miles is passed over, a bell gives notice of the 

 working machinery lieing disengaged : the section is removed, a fresh sheet 

 of paper is introduced, and, as the pencil maintains its position, the section 

 ivill be carried on continuously. 



This communication is accompanied by three working drawings, showing, 

 on a large scale, the machine in action, and all the component parts in great 

 detail. 



" On the Efflux of Gaseous Flmdn under presmre." By Charles Hood, 

 F.R.A.S., &c. 



The theoretical determination of the velocity with which gaseous fluids 

 are discharged through tubes and apertures, has frequently been investigated 

 by mathematicians ; and as the question is one of importance in various 

 branches of practical science, tlie author examines the several theorems which 

 have been proposed for its elucidation, and compares them with the results 

 obtained by experimental researches. 



Dr. Papin, in 1G86, appears to have first ascertained the law of efflux to 

 be the same for both elastic and inelastic fluids, and the majority of the 

 writers on the subject since his tin],* have adopted as the fundamental data 

 of their calculations, the hydrodynamic law of sponting fluids, by which the 

 velocity of discharge is found to be proportional to the square root of the 

 height of the superincumbent column of homogeneous fluid. 



The author investigates particularly the methods of calculation proposed 

 by Dr. Gregory, Mr. Da\ies Gilbert, Mr. Sylvester, Mr. Tredgold, and M. 

 Montgolfier. and points out the differences which exist in their several 

 methods. Tliat of Mr. Sylvester is the only one which differs in any con- 

 siderable degree from the simple law above stated ; and his calculation is 

 based upon the supposition that the respective columns of light and hea\-v 

 air represent two unequal weights suspended by a cord, hanging over a 

 pulley — by which mode of calculation, in the cases selected by the author 

 for comparison, a result is obtained of only aljout one-third the amount given 

 by the other methods. These calculations are compared with some experi- 

 ments made by Sir John Guest at the Dowlais Iron Works, and also of Mr. 

 Dufreuoy at the Clyde and at the Butterly Iron Works, recorded by him in 

 his report to the Director-General of Mines in France. The results are tabu- 

 lated : giving the pressm'e of the blast, the area of discharge, the velocity of 

 the blast, tlie quantity of air ascertained by experiment, and the quantity 

 shown by the several methods of calculation. From all these comparisons 

 the author draws the conclusion that the method of calculation proposed by 

 Montgolfier is the most accurate' as it is also the most simple. If the pres- 

 sure be ascertained in inches of mercuiy, it is only necessar.' to find the 

 column of air in feet equivalent to the pressure, and to multiply this number 

 (as in the common case of gravitating bodies) by 64 feet, and then the square 

 root of this product will give the velocity of discharge in feet per second. 

 The equivalent height of the column of air in feet is found by multiplying 

 the number of inches of mercury by 11,2.30 and dividing the product by 12, 

 mercury being 11,230 times the weight of air. .^llowiug for a small loss by 

 friction in the quantity found by experiment, the agreement between the 

 theoretical and experimental quantities is extremely near. Rules are like- 

 wise given for applj-ing these calculations to other gases of different specific 

 gravities, which are also applicable to chimney draughts and to the expansion 

 of air by heat. 



ExD OF Session 1840. 



BKITISH ASSOCIATION FOR THE ADVANCEMENT OF SCIENCE. 

 Texth Meeting. — September^ 1840. 



(From the AtheTupmn.) 

 Section G. — Mechanical Science. 



" On certain Imjirm-ements on Locomotive and other Engine Boilers." By 

 Mr. Hawthorn. 



The object of this improvement is to prevent what is teclmically called 

 " priming," to heat the steam on its passage to the cylinder, and to employ 

 return tubes, as well as direct tubes, for heating the water. The advantages 

 are said to be, that no water is carried with the steam into the cyhnder, and 

 a saving of fuel, tlirough the arrangement of the tubes, from 30 to 40 per 

 cent. 



Mr. Scott RusseU observed, that the plan of surcharging steam was much 

 used in America. They work the steam expansively. Mr. RusseU thought 

 the dome shape in the fire-box inferior to the ^at staged box, and was afraid 

 that the steam, returning from the cylinder through the boiler, would merely 

 abstract and not communicate heat. 



** 071 the Fan-htast as applied to Furnaces" By Mr. Fairbairn. 



In explaining the methods to be pursued in adapting furnaces to the fan- 

 blast, Mr. Fairbairn obsei-ved that it was well known that its application to 

 the cupola for melting pig iron was attended with the most complete success ; 

 and the object of the present inquiry was to determine how far the same 



mode of blowing was apjilicable to furnaces on a large scaie. for the imq>ose 

 of smelting ores. Objections had been made to Jlr. Fairhairn's plan, on ac- 

 count of tlie veiT low pressure at which the air is introduced into the furnace, 

 and its insufticiency to force it throngh a mass of material such as is contained 

 in the fmnaces of this country, and which is from 30 to 40 feet in depth. 

 To these objections Mr. Fairbairn replied, that the same had been urged 

 against the introduction of the fan-blast to the cupola : that, in his opiniou, 

 its efticieucy was as the quantity discliarged, and not the pressure, wliich 

 regulated the passage of the air from tlie " twyres '' to the top of the furnace. 

 Tlie fan-l)last, when supplied with large apertures into the furnace, would, in 

 his opinion, increase the process of calcination, eflect a more equable tempe- 

 rature, and produce a suiierior quality of metal. It appeared, therefore, of 

 importance that the experiment should be made, and Mr. Fairbairn offered to 

 superintend its introduction, provided the pro])rietors of the numerous works 

 in this country agreed with him in opinion, that the process would be advan- 

 tageous both as regards expense, and the improved quality of the metal pro- 

 duced. 



Mr. Smith thought the plan well worthy of being tried. It is not the 

 force of the blast that is necessary, but the quant itij of air introduced. In a. 

 cupola in which the blast is given by the fan, the iron is brought down ii» 

 h.Tlf the time that was necessary with the cylinder blast. Mr. Smith has no 

 doubt of the success of the fan-blast in smelting furnaces, the heat being; 

 more miiform. 



" On Propelling Boats on Canals." By Mr. Smith. 



Mr. Smith proposed that the steam power in the boat should drive two 

 large wheels, of thirty feet diameter, which should bite the ground at the 

 bottom of the canal. He exhibited a working model on this principle, which 

 succeeded on the small scale ; and he stated that he had tried it on a larger 

 scale with the powei' of four men, and it had also succeeded. The wheels 

 might be either on each side of the boat, as in the model, with a provision 

 for a play of three or four feet, that they might accommodate themselves to 

 inequalities at the bottom of the canal : or there might be one wheel in the 

 centre of the boat, if constructed on the twin ]>rineip!e. 



Mr. Scott Russell was not sanguine as to the success of this plan. The 

 wheels must be made very lieavy, in order to give tlie piopelling power, and 

 their weight would have an injurious effect at the bottom of the canal. A 

 large steam boat would be necessary in order to get sufficieut power, and if 

 this large vessel were propelled at high velocities, the surge from the bows 

 would be very great, and the stent would drag in the water. — Mr. Smith said, 

 that he had confidence in the plan, notnithstanding the objections raised, 

 and intended to try it on a large scale, and would report next year to the 

 Association the results, whether favourable or otherwise. — Mr. Glynn re- 

 marked, that an attempt was made some years ago by Mr. Seaward, to propel 

 boats on canals by means of wheels composed of two rims, with steps be- 

 tween them as a ladder, running on the bottom of the canal ; but it was 

 abandoned. 



" On a New Rain Gauge." By Mr. James Johnston, of Greenock. 



Mr. Johnston described anew rain gauge, so constructed that the receiring 

 funnel or orifice at which the rain enters, is always kept at right angles to the 

 falling rain. By the action of the wind on a large vane, the whole gauge is 

 tiu'ned roimu on a pivot, until tiie front of the gauge faces the quarter from 

 whence the wind blows ; and by tlie action of the wind on another vane at- 

 tached to the receiving funnel, the mouth of the fminel is moved from a 

 horizontal towards a perpendicular position according to the strength of the 

 wind. The receiving funnel and vane attached to it are lialanced with coun- 

 terpoise weights, in such a manner that the wind, in moving them, has as 

 much weight to remove from a perpendicular position, in proportion to their 

 bulk, as it has when moving an ordinary sized drop of rain from the same 

 position ; by this means the mouth of the gauge is kept at right angles to the 

 falling rain. 



Mr. Milne gave an account of a High Pressure Filter for Domestic Pur- 

 poses. — Mr. Thorn stated, that from experience he found it was better to 

 filter downwards than upwards. — Mr. Hawkins agreed with Mr. Thom, that 

 filtration downwards is superior to filtration upwards ; he preferred charcoal 

 to sand for filtering, and preferred filtering without high pressure. 



Mr. Dunn explained Ponton's Electro-Magnetic Telegi'aph, which instru- 

 ment was exhibited in the model room. 



Mr. Fairbairn described Hall's Patent lladraulic Belt for Raising Water. 



M. le Comte de LiUe explained his method of laying down Wood Pave- 

 ment, as exemplified at Whitehall. 



The Rev. Dr. Paterson gave an account of an Improved Life Boat, which 

 he called a Riddle Life Boat, because the bottom is like a riddle. The sides 

 of the boat consist each of a hollow elliptical tube, to be made of sheet -iron, 

 and from this it has all its buoyancy, which is unaffected by any influx of 

 water. This boat, he said, was light', easily propelled, and drew only a foot 

 or two of water : and besides being used for reaching vessels in distress, or 

 carrying passengers to steam boats, it might be itself carried as a ship's boat 

 — to be ready for use in danger, or difficidt landing. 



Mr. Williams stated, that this boat seemed to be original, and that he (Mr. 

 WUhams) would make a trial of it on a large scale.— Mr. Vigaoles thought it 

 might be usefully employed for pontoons. 



" On an Improved Rain Gauge." By Mr. Thom. 



It consists of a cylinder two feet long, and seven inches diameter, sunk iu 



