The Conductivity of Heat Insulators. 



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violet, the sensation equation to white was determined. The other 

 colours of the spectrum were then used in forming white, and from 

 their luminosity equations their percentage composition in sensations 

 were calculated. The percentage curves are shown. The results so 

 obtained were applied to various spectrum luminosity curves, and 

 the sensation curves obtained. The areas of these curves were found, 

 and the ordinates of the green and violet curves increased, so that 

 both their areas were respectively equal to that of the red. This gave 

 three new curves in which the sensations to form white were shown by 

 equal ordinates. 



A comparison of the points in the spectrum where the curves cut 

 one another, and of those found by the red and green blind as matching 

 white, show that the two sets are identical, as they should be. 

 The curves of Koenig, drawn on the same supposition, are called attention 

 to, and the difference between his and the new determination pointed 

 out. 



The red below the red lithium line, as already pointed out, excites 

 but one (the red) sensation, whilst the green sensation is felt in greatest 

 purity at A. 5140, and the blue at A 4580, as at these points they are 

 mixed only with the sensation of white, the white being of that 

 whiteness which is seen outside the colour fields. 



"The Conductivity of Heat Insulators." By C. G. Lamb, M.A., 

 B.Sc, and W. G. Wilson, B.A. Communicated by Professor 

 Ewing, F.B.S. Beceived May 3 —Bead June 15, 1899. 



The comparative efficiency of materials used as insulators has been 

 the subject of several investigations ; the majority of these have been 

 conducted at fairly high temperatures, and it may be questioned 

 whether the results can be applied to the same materials when used as 

 a lagging to protect bodies at low temperatures. Moreover the 

 methods adopted do not seem susceptible of any considerable accuracy. 

 The method to be described was devised with the object of using 

 lower temperatures and smaller ranges than had been used in previous 

 experiments, to attain a perfectly steady state of heat transference, 

 and allow of greater accuracy and simplicity in the measurements. 



The substances selected for experiment so far have been those which 

 could easily be tested in the dry state, without being made up into 

 cements; they include air, sawdust, charcoal, pine shavings, paper, 

 asbestos, sand, silicate cotton, hair felt, rice husks, and a heat insulator 

 known as " kapok." 



The method employed consisted in placing the material under test in 

 the space between two cylindrical copper pots, kept at a definite distance 

 apart by pieces of vulcanised fibre ; the inner pot contained a small 



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