SCIENTIFIC SUMMARY. 
517 
A Defect in the demonstrating Polariscope , and a remedy for it, have been 
discovered by Mr. J. Trail Taylor, the well-known editor of the British 
Journal of Photography. Mr. Taylor read a short paper upon his discovery 
at the last British Association meeting. He stated that his observations of 
polarized light projected on a screen, led him to discover that even the best 
instruments constructed are liable to error, inasmuch as none but the axial 
rays transmitted through the condensers are polarised, the main body of the 
luminous cone undergoing reflection from the polariser without being really 
polarised. He remedied this by intercepting the light with a flint concave 
lens before it reached the polariser, so that the whole mass of rays being 
projected in a parallel direction was completely polarised. On leaving the 
polariser the rays were again converged before passing through the crystal or 
other object to be exhibited, by a small achromatic lens which thus .acted as 
an achromatic condenser. It was stated that this arrangement effected a 
most important increase in the brilliancy of the object exhibited on the 
screen. 
The Production of Ozone. — M. G. Plante has found that during the electro- 
lysis of water much more ozone is produced when the electrodes are of lead 
than when they are of platinum, in fact, nearly half as much again. He 
considers that the explanation is rather difficult, but he attributes it to the 
presence of a layer of oxide on the electrode, which thus gives rise to a 
secondary action. — Vide Comptes Bendus, July 23rd. 
The Heat-conductibility of Mercury. — M. Gripon, who has been making 
experiments after Peclet’s method, thinks he has demonstrated that if the 
conducting power of silver be regarded as 100, that of mercury is equal 
to 3 - 54. He places mercury, therefore, the lowest in the scale of metals, 
as far as the conductibility of heat is concerned. It is strange that electric 
conductivity is quite different, being represented by the figures 1 *80. 
Penetration of Platinum and Iron by Hydrogen. — From time to time we 
have reported the discoveries of Troost and Deville in this field of research. 
These conclusions have recently been collected by the Master of the Mint, 
Mr. Thomas Graham, in an admirable paper published in the Proceedings of 
the Boyal Society. He thinks that this wonderful penetration is connected with 
a power resident in the above-mentioned and certain other metals to liquify 
and absorb hydrogen, which latter is possibly in the condition of a metallic 
vapour. Platinum in the form of wire or plate at a low red heat may take 
up and hold 3'8 volumes of hydrogen, measured cold ; but it is by palladium 
that the property in question appears to be possessed in the highest -degree. 
Palladium foil from the hammered metal, condensed so much as 643 times its 
volume of hydrogen, at a temperature under 100° C. The same metal had 
not the slightest absorbent power for either oxygen or nitrogen. The capacity 
of fused palladium (as also of fused platinum), is considerably reduced, 
but foil or fused palladium, a specimen of which Mr. Graham obtained from 
Mr. G. Matthey, absorbed 68 volumes of the gas. Mr. Graham thinks 
that a certain degree of porosity may be admitted to exist in all these metals, 
and to the greatest extent in their hammered condition. It is also thought 
that such metallic pores, and, indeed, all fine pores, absorb hydrogen very 
rapidly, especially in the liquid condition. Hence Mr. Graham concludes that 
the phenomenon of penetration above alluded to, may be explained by sup- 
