1839.] 



*rSE CIVIL ENGINEER AND ARCHITECT'S JOURNAL, 



18d 



dest. In a composition a strict equality nuist be preserved in these 

 variations of shade, tint, and hue. 



Light holds a most intimate connection, botli in its constitution and 

 operations, witli all the other sciences, and must ultimately attain a 

 most important rank among the sciences, and repay back to them what 

 it has received from them. Many of the phenomena are only to be ex. 

 plained by reference to hydro-dynamic principles, and it is from them 

 that the undulatory theory, under the fostering care of Young, attained 

 its present preponderance. The relation of the laws of light to 

 acoustics and music are most astonishing in their resemblance ; and 

 Field, has arranged octaves of a musical and chromatic. Tiie 

 phenomena called polarised light, however hcauliful, are not con- 

 lined in their application to an entertaining exhibition, but 

 present philosopliers wiiii the most delicate instnnnents for as- 

 certaining the constitution of bodies. It is an optical law that all 

 transparent bodies become coloured when they are formed info plates 

 attenuated beyond certain limits, and moreover, that the particular 

 colours, which under these circumstances they show, are depen. 

 dent upon the degree of attenuation. It was tluis that Newton de- 

 termined that the thickness of the thinnest part of the soap-bubble, 

 wlien colours are lirst visible, is DO more than ^j~i of an inch, and 

 that before it bursts it attenuates to -rrrT^}- — ; and by the same 

 means we know that the transparent wings of some insects are not 

 more than foi'j^o of an inch in thickness. For an admirable expla- 

 nation of tlie laws of interference, and for a beautiful apparatus for 

 polarising light, for which he received the silver medal, we cannot do 

 better than to rcl'cr to tlie paper, No. 1, of Mechanics on the "Trans- 

 actions of the Society of Arts," by Mr. Goddard, of the Polytechnic 

 Institution. In this he ably demonstrates all the paradoxes of waves 

 producing stillness ; sound, silence ; and light, darkness. 



The chemical relations, however, present features which become of 

 practical interest to the architect and engineer, and their full extent is 

 yet unascertained. M. Mitzcherlich observed that light inHuenced 

 crystallisation, and produced dimorphism, and from prismatic forms 

 changed the crystals of sulphate ol* nickel into that of the square octa- 

 hedron, without any apparent change in external form or appearance. 

 Light appears to possess two properties, sometimes separate and some- 

 times conjoined ; namely, that of illumination, and that of warmth. 

 Herschel, WoUaston, Rittcr, and Scheele have shown that there are 

 ra)'s transmitted from the sun which do not illuminate, and yet produce 

 more heat than the visible rays, while there are other invisible rays dis- 

 tinguished by their chemical effects. Scheele discovered that a glass 

 mirror, held before the fire, reflected the rays of light, but not those of 

 calorie ; but that when a metal minor was placed in the same position, 

 both light and heat were reflected. Herschel found that the invisible 

 rays emitted by the sun have the greatest heating power. In an expe- 

 riment on the heating power of the different rays of the spectrum, he 

 found that when the thermometer was placed out of the range of the 

 colored rays, it rose still higher than in the red ra\', which he considered 

 the strongest ; the heating power of these invisible rays was greatest 

 at the distance of half an inch beyond the red ray, but it was sensible 

 at the distance of an inch and a-half. The relative powers of colours 

 itj absorbing light and heat vary very much ; and Franklin's experiment 

 illustrative of this is well known : — He laid on the snow four pieces of 

 paper, white, yellow, blue, and black, and when he went to see the 

 effect, he found that the black paper had sunk an inch or two deep, 

 the blue a good deal, the yellow very little, the white not at all. The 

 relative chemical power of the several colours is not however known, 

 very few experiments having been made, and those conflicting. Mrs. 

 Sonierville considered the violet ray as the strongest, and the green as 

 the most sluggish ; and the experiments of Mr*. Robert Mallet, related 

 last year before the British Association, are to the same effect. He 

 gives the following as the period of complete decoloration of recent 

 solutions of caustic potass, by the chemical action of light under differ- 

 ent shades : — 



Violet glass exposed to air 



Ditto closed 



Transparent flint glass 



Ditto closed . 



Yellow 



Blue 



Orange • , > 



Red 



Green unchanged in 



30 hours 



SO 



80 

 115 

 170 

 185 

 190 

 200 

 200 



The recent experiments of Sir John Herschel, however, lead lis to 

 expect very different results, and the establishment of more satisfactory 

 laws. The way, in wliich his law ofcoloiir acts as an agent or reagent 

 in economical pursuits will perhaps however be better illustrated by 

 e.xtracts from the following able paper by Mr. W. Kennish, carpenter 

 on board H.M.S. Victory, at Portsmouth, at p. 101. of the " Transactions 

 of the Society of Arts ;"-^ 



There is noDiing that will prove this evil more than by observing the black 

 streaks of a ship after being in a tropical climate for any length of time. It 

 will be found tfiat the wood round the fastenings is in a state of decay, while 

 the while work is as sound as ever: the planks that arc painted black will be 

 found split in all directions, while the frequent necessity of caulking a ship in 

 that situation likewise adds to Ihc common destruction ; and I am fully per- 

 suaded, th.1t a piece of wood painted wliitc will be preserved from perishing 

 as long again, if exposed to tiie weather, as a similar piece painted black, 

 especially in a tiopical climate. 



I have heard many men of considerable experience say, that black is gooil 

 for nothing on wood, as it possesscB no bodff to exclude the weather. This is, 

 indeed, partly the case ; but a far greater evil than this attends flie use of 

 blacU paint, which ought entirely to exclude its use on any work out of doors, 

 viz., its property of absorbing heat. A black unpolished surface is the great- 

 est absorber and radiator of heat known ; while a white surface, on the other 

 hand, is a bad absorber and radiator of tlie same ; conbequently, black pain 

 is more pernicious to the wood than white. * # , * 



Wood, having a black surface, will imbibe considerably mo're'heat in the 

 same temperature of climate than if that surface was white ; from which cir- 

 cumstance we may easily conclude, that the pores of wood of any nature will 

 have a tendency to expand, and rend in all directions, when exposed under 

 such circumstances, — the water of course being admitted, causes a gradual 

 and progressive decay, which must be imperceptibly increasing from every 

 change of weather. Tlie remedy to so great an evil is particularly simple, 

 viz., by using white, instead of black paint, which not only forms a better 

 surface, but is a preventive to the action of heat, and is more impervious to 

 moisture. The saving of expense would also be immense, and I aui convinced 

 that men of practical experience wiU bear me out in my assertion. 



Two striking circumstances, which have fallen under my own immediate 

 notice, deserve mention. The tirst was tlie state of H. M. Sloop Ringdove, 

 condemned by survey at Halifax, N.S., in the year 1828. 



This brig iiad been on the West India station for many years. Uu lur 

 being found defective, and a survey called, the report was to the effect thai 

 the wood round all the fastenings was totally decayed in the wake of the 

 black, while that in the wake of the white was as sound as ever; a striking 

 proof of the dift'erent efl'ect of the two colours. 



The next instance I shall mention relates to H. M. Ship Excellent, of 98 

 guns (formerly the Boyne). 



This ship is moored east and west, l)y bow and stern moorings; con- 

 sequently, tire starboard side is always exposed to the effects of the sun, both 

 in summer and winter, hi this situation her sides were pair,ted in the usual 

 manner of a ship of war, viz., black and white, of which by far the greater: 

 part is black; this latter portion on the starboard side I found it impossible to 

 keep tight; for, as often as one leak was apparently stopped, another broke 

 out, and thus baffled the skill of all interested. In the meantime, the side not 

 exposed to the rays of the sun remained perfectly soimd. I then suggested to 

 Mr. Kenuaway (the master caulker of her Majesty's dockyard at Portsmouth')', ' 

 whohad previously given the subject consideration, the advantage likely to be' 

 derived from altering the colour of the ship's side from black to white 

 Captain Hastings having approved of the alteration, the ship was painted a • 

 light drab colour where it was black before, upon which the leaks ceased, and 

 she has now continued perfectly tight for more than twelve months ; and, 

 indeed, I can confidently state that the ship will last as long again in her 

 present situation, as she had begun to shrink and split to an astonishing, 

 extent when the outside surface was black, and which has entirely ceased 

 since the colour was altered. 



This result of black we may readily believe, when we recollect] 

 Saussiire's cxpciimcnts on the Alps, when he placed on a mountain a ' 

 box, lined with black cloth, with the side next the sun, closed by three 

 panes of glass at a little distance apart the one from the other, and 

 found the thermometer rise ;jOo in two hours from the concentration of" 

 the sun's rays. We might give a greater number of examples, and ' 

 particularly of the manner in which it bears upon agriculture, but it 

 may perhaps be sufficient if we remind our readers tliat Mr. Kcnnish's 

 experiinent is going on at a fearful scale on many extensive pieces of , 

 woodwork, to which the attention of architects and engineers might be ^ 

 dfrt'JtoJ. ■" '■' 



Jilr; Hay's book is the fourth edition of a work decidedly esteeme'tf"- 

 ibr its practicability, cheapness, and the soundness of its principles, and" 

 '"o' it is added in this edition an excellent Treatise on House-painting. '■ 

 li. is indeed the clieapest and best work on the subject, and one to 

 which our readers of all classes may refer with advantage and deliglit. 



■ 'Tb'diftuse a taste for this neglected branch of art, and wc should be 

 indeed pleased to see the people waken up from this lethargy and call 

 on otir architects to revive the beauties of internal decoration. King 



1 o<us' architects are alive in Bavaria, painting houses, inside and out, • 

 : u'lithochromy, and why should painting in England remain where ifi " 



■ vife iB Sir James Thornhill's time, at the top of the dome of St. Panl'Si. ' ' 

 nstead of being in our palaces, our piiWic buildings, and our houses. 



A' Practical Treatise on Brirl^e BuiMiiK/. By E. Cresy, Esq. Arch,. 

 C.E., F.S.A,, &c. London 1 .John Williams. _ ■iiiw 



We hail with pleasure the appearance of this work on Bridget] ' 

 which is got up witli great care, and with numerous plates, beautifully 



