682 
Proceedings of the Royal Society 
in existence in European and American collections. That both are 
of great value no one can doubt. Indifferent skins may be worth 
from eighty to one hundred guineas, and indifferent examples of 
the egg more than half that sum. A really fine specimen of the egg, 
blown at the side, if there he one in existence, must be valued at 
its weight not in gold, but in hank notes. No wonder, then, that 
unprincipled persons have been known to imitate both egg and skin 
— the counterfeit egg especially being a consummate work of art. 
Although much has been written of late years about the Garefow], 
a complete monograph on this extinct bird is still a desideratum in 
scientific literature ; and ornithologists have for some time been in 
expectation of seeing such a work produced. The name of Professor 
Newton of Cambridge University has been mentioned, and naturalists 
of all nations allow that the task of writing the Great Auk’s 
memorable history could not be committed to abler hands. 
5. On a New Telephone Eeceiver. By Professor Chrystal. 
The experiment which forms the subject of this communication 
was originally devised as an illustration of the explanation of all 
kinds of microphone receivers, suggested by the beautiful experi- 
ments of Mr Blyth, on loose contacts. My idea was to replace 
Mr Blyth’s heated point of metal by a continuous portion of the 
circuit which should act in the same manner. 
It was obvious, for two reasons, that this part must he of small 
diameter ; ls£, in order that the resistance, per unit of length, might 
be great enough to make the variation of the heating sufficient to 
cause sensible longitudinal extension ; 2 d, in order that the section 
might be small enough to allow sensible cooling in, say the -g-solh 
of a second. I had reason beforehand to believe that the second 
of these conditions could be fulfilled in practice ; because, I found 
in my experiments on Ohm’s Law (Brit. Ass. Rep. 1876, p. 58, et 
seq.) that, when currents of two different strengths alternated, even 
with great rapidity (60 times per second) in a fine wire, the 
resistance was sensibly higher during the passage of the stronger 
current. 
My first experiment was tried with Mr Blyth’s apparatus. A 
fine platinum-iridium (10 p. c. Ir. Res. • 7 Ohm per Cm.) wire, about 
