1843.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



323 



been built, under the direction of Mr. Darlington, with cylinders of 50 inches 

 diameter, and 10 feet stroke, worked by a force of water of 22 fathoms, 

 through a descending column of 30 inches diameter ; the pumps worked by 

 the engine were -42 inches in diameter, raising water from a depth of 22 

 fathoms; the usual speed of working was four strokes per minute, hut he 

 had seen it attain six strokes. The concussion produced by the closing of 

 the valve at the end of the stroke, was generally very prejudicial to these 

 engines ; but in that made by Mr. Darlington, it was diminished by allowing 

 the large valve to close a short time before the stroke finished, and bringing 

 the piston home with a small valve; by this means no noise was heard be- 

 yond that of the rush of the water, and the violent shocks were avoided. 



BRITISH ASSOCIATION FOR THE ADVANCEMENT OF SCIENCE. 

 Thirteenth Meeting, 1843. — Held at Cork. 



" On the Application of our Knowledge of the Laws of Sound to the Con- 

 struction of Buildings." By Mr. Scott Russell. 



The object of this paper was twofold — first, to apply our knowledge of the 

 known laws of sound to the phenomena of speaking and bearing in a given 

 building; and secondly, to develop certain laws of sound recently discovered, 

 and not generally known ; and to show their application to the same prac- 

 tical purposes. Part I. of the paper contained the application of the known 

 laws of sound to the construction of buildings. The author prefaced this 

 part of the paper by describing a form of building which had been found to 

 be perfectly adapted to the purpose of seeing and bearing with distinctness 

 and comfort. This arrangement of buildings bad been described by him 

 in a paper communicated to the Royal Society of Arts of Scotland some 

 years ago, but had not been actually constructed on a large scale until lately, 

 when a young architect, Mr. Cousins, of Edinburgh, having been employed 

 to construct some large buildings, and alighting on this paper, adopted its 

 principles. Buildings were now erected on this principle, and contained 

 from fifteen hundred to three thousand people, whom they accommodated 

 without difficulty, and with perfect comfort both to speaker and hearer. 

 He had little doubt, from experiments he had recently made, that so many 

 as ten thousand people might be so arranged as to hear with ease and com- 

 fort a good speaker. Mr. Scott Russell's principle of construction is to 

 place the speaker in the focus of a curve, which be calls the curve of equal 

 hearing, or the isacoustic curve ; and to place the seats of the auditors in 

 such a manner that their heads shall all he arranged in this curve. 



" Let A B C D represent the vertical section of a building for public speak- 

 ing, S the height of the speaker on his platform, D C the floor of the build, 

 ing; then, for the purpose that all the auditors should hear and see equally 

 well, they should be placed on the line S R B of the acoustic curve. This 

 curve is constructed in the following manner : — D Cis first divided into equal 

 parts to represent the usual breadth of a sitting, and vertical lines are drawn 

 through these points. R being the place of the auditor 1 , the place of auditor 

 2 behind him is assigned thus — join S R, and produce it to a — from a upwards 

 set off a 2 = 9 inches, and 2 is the proper height of the next spectator. Then 

 join S 2, produce it to b, and set off A 3 = 9 inches, and 3 is the place of the 

 third spectator, and so on for the place of every spectator. Such was the 

 vertical section of the building. The horizontal section was either circular 

 or polygonal, having the speaker at the centre. This form had been found 

 perfectly successful in affording the highest degree of comfort both to hearer 

 and speaker ; therefore he submitted it with confidence to the section, as a 

 practical ami established principle, more than as a mere theoretical specula- 

 tion. The remainder of this paper was then adjourned till the next day. 



" Chromotype, a neiv Photographic Process." By Mr. R. Hunt. 



We are indebted to Mr. M. I'onton for the discovery of the first photo- 

 graphic process in which chromic acid was the active agent. He used a 

 paper saturated with the bichromate of potash, which, on exposure to sun- 

 hine, speedily passed from a fine yellow colour into a dull brown, giving, 



consequently, a negative picture. E. Becquerel improved upon this process, 

 by sizing the paper with starch previously to the application of the bichro- 

 mate of potash, which enabled him to convert the negative picture into a 

 positive one by the use of a solution of iodine, which combined with the 

 starch in those parts on which the light had not acted, or acted but slightly, 

 forming the blue iodide of starch. These pictures are, however, tediously 

 produced; they are seldom clear and distinct, and failure too frequently 

 follows the utmost care. While the author was pursuing an extensive series 

 of researches on the influence of the solar rays on the salts of different 

 metals, he was led to the discovery of a process by which positive photo- 

 graphs are very easily produced. Several of the chromates may be used in 

 this process ; but the author prefers those of mercury or copper, the most 

 certain effects being produced by the chromate of copper, and, indeed, in a 

 much shorter time than with any of the other chromates. The papers are 

 thus prepared ; good writing paper is washed over with a solution of the 

 sulphate of copper and partially dried ; it is then washed with a solution of 

 the bichromate of potash and dried at a little distance from the fire. Papers 

 thus prepared may be kept for any length of time, and are always ready for 

 use. They are not sufficiently sensitive for use in the camera obscura, but 

 they are available for every other purpose. An engraving — botanical speci- 

 mens or the like — being placed upon the paper in a proper photographic 

 copying frame, it is exposed to sunshine for a time, varying with the intensity 

 of light from five to fifteen or twenty minutes. The result is generally a 

 negative picture. This picture is now washed over with a solution of nitrate 

 of silver, which immediately produces a very beautiful deep orange picture upon 

 a light dun colour, or sometimes perfectly white ground. This picture is 

 quickly fixed by being washed in pure water aud dried. The author remarked 

 that, if saturated solutions were used, a negative picture was first produced, 

 but if the solutions were diluted with three or four times their bulk of water, 

 the first action of the sun's rays was to darken the paper, immediately upon 

 which a very rapid bleaching action followed, giving an exceedingly faint 

 positive picture, which was brought out in great delicacy by the nitrate of 

 silver. It is necessary that pure water should be used for the fixing, as the 

 presence of any muriate damages the picture, and hence arises another pleasing 

 variation of the chromatype. If the positive picture be placed in a very weak 

 solution of common salt, the images slowly fade out, leaving a very faint ne- 

 gative outline. If it be taken from the solution of salt and dried, a positive 

 picture of a lilac colour may be produced by a few minutes' exposure to sun- 

 shine. Prismatic analysis has shown that the changes are produced by a class 

 of rays which lie between the least refrangible blue, and the extreme limits of 

 the violet rays of the visible prismatic spectrum — the maximum darkening 

 effect being produced by the mean blue ray, whilst the bleaching effect appears 

 to be produced with the greatest energy by the least refrangible violet rays. 



" On the Construction ofLuntley's Shadowless Gas-burners, and the Shape 

 of Glass Chimneys for Lamps." By Mr. H. Dircks. 



The object of the burner was to bring the gas issuing from the small 

 orifices into direct contact with atmospheric air at the ordinary temperature. 

 Mr. Dircks contended that the heating of the air previously to its combus- 

 tion diminishes the brightness of the flame ; because, while each volume of 

 carburetted hydrogen gas requires ten volumes of atmospheric air for its per- 

 fect combustion, the expansion of the air by heat necessarily reduces the 

 weight of oxygen contained in the same volume of air ; and therefore unless 

 some means be adopted of increasing the supply of air, the oxygen would be 

 deficient. Another alleged advantage of the burner arises from the small 

 quantity of metal through which the orifices are perforated, for by that 

 means a smaller quantity of heat is abstracted in burning. The peculiarity 

 in the form of the glass chimney consists in having the upper end enlarged. 

 The effect of this enlargment, Mr. Dircks said, was to open the top of the 

 flame and increase its brightness. 



Mr. J. Taylor explained to the meeting the recent improvements of Dr. 

 Faraday in the combustion of gas ; and a short discussion arose, in which 

 Mr. Hawkins and Dr. Scoresby took part, on the advantage of enlarging the 

 upper ends, not only of glass chimneys, but of all chimneys for the com- 

 bustion of fuel." 



Tidal Observations. 



Mr. J. S. Russell read a report of his observations on the tides of the 

 Frith of Forth and the cast coast of Scotland. The especial object of this 

 series of investigations was to discover fully the nature and causes of some 

 remarkable tides which exist in the Frith of Forth, and to connect them with 

 observations ou the adjacent tides, and likewise furnish some better data for 

 the construction of practical tide tables for predicting the time and height 

 of high water at these places. The methods of observation were distinct from 

 those which bad previously been made. Instead of merely observing the 

 periods of high and low water, observers were placed to note the rising of 

 the water every five minutes, night and day, for several weeks and months 

 together. This was done at twelve places simultaneously, from Newcastle 

 along the coast to Inverness, so that from 2,000 to 3,000 observations were 

 got from the stations in the course of a day. These were daily transmitted 

 to the central station, and immed ately laid down geometrically ou ruled 

 paper, so as to represent graphically to the eye the outline of each tidal wave 

 by a curve. From the form of the curve it was that the most important 



41 



