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Proceedings of the Royal Society 
a curve to tlie right or to the left; the third space, between lines 
3 and 4, represented 20 seconds of continued action of light, during 
which the electro-motive force gradually rises ; and, lastly, the fourth 
space, between lines 4 and 1 (the point of starting) represents 20 
seconds, during which the electro-motive force at first rises on the 
withdrawal of light and afterwards sinks rapidly. 
5. On the Thermo-electric Properties of Pure Nickel. 
By Professor Tait. 
By the kindness of M. de Boisbaudran I have been enabled to 
experiment upon a specimen of nickel, very nearly pure. Its 
thermo-electric relations are exceedingly interesting, and are easily 
observed by employing palladium as the second metal in the 
circuit. The nickel line in the thermo-electric diagram presents 
nearly the same appearance as that of iron, but its peculiarities 
occur at much lower temperatures. 
Speaking generally, at low temperatures it is nearly parallel to 
the palladium line, but below it ; the specific heat of electricity 
being negative. The specific heat changes sign about 230° C., and 
thereafter the nickel line intersects the palladium. Shortly after 
this intersection (at about 340° C.) the specific heat again becomes 
negative, and of nearly its first amount ; so that the lines are 
again parallel, but nickel is now above palladium. These curious 
facts are probably connected with the magnetic properties of iron 
and nickel, possibly also with the chemical distinction of ferricum 
and ferrosum. But exact determinations (which I hope soon to 
make) are required before such speculations can be successfully 
carried out. 
6. Notice of the Bavages of the Limnoria terebrans on 
Greenheart Timber. By David Stevenson, Civil 
Engineer. 
In 1862 I communicated to the Society a notice of the ravages 
of the Limnoria terebrans on timber employed in engineering 
structures exposed to the action of the sea. In that communica- 
tion I stated that African, English, and American oaks, maho- 
gany, teak, beech, ash, elm, and the different varieties of pine, were 
found sooner or later to become a prey to the Limnoria. The 
