270 Proceedings of the Royal Society. 
when broken down. The longest period which the author has ob- 
served the amputated organ to continue luminous is 20’, and it 
continues to shine in media of very different properties, in vacuo, 
under mercury, in water, and in oil. The light is re-excited by 
certain irritants ; by heat and cold, by friction and by galvanism, 
by alcohol, camphor, and ammonia. In the living animal, also, 
mechanical and chemical stimulants excite the appearance of the 
light provided they do not disorganize the part. When the animals 
are killed by alcohol, tincture of hellebore, or of nux vomica, and. 
certain other poisons, after all light and life have ceased, another 
fixed and steady light appears in the organ, varying in duration 
from 12 hours to 4 days. From the general results of his obser- 
vations, the author concludes that the luminous powers of these 
insects are exclusively referable to vital action, and that their 
use has not been accurately ascertained, though probably con- 
nected with sexual distinction. . 
Sir F. Shuckburgh, Bart. was admitted a fellow. 
The society then adjourned over two Thursdays, to meet again 
on the 29th of April. 
Thursday, April 29. 
The Rey. Dr. Maltby and E. H. Lushington, Esq. were admitted 
Fellows. 
A letter from Dr. Tiarks to Dr. Young was read, containing 
A short Account of some Observations made with Chronometers, 
in two Expeditions sent out by the Admiralty, at the recommenda- 
tion of the Board of Longitude, for ascertaining the Longitude 
of Madeira and of Falmouth. 
Dr. Tiarks was sent out to Madeira, in the year 1822, with 
fifte.2 chronometers, of which the rates had principally been as- 
certained in the Royal Observatory at Greenwich; he touched at 
Falmouth both in going out and in returning; and having again 
ascertained the rates of his time-keepers, he was thus enabled to 
obtain two distinct determinations of the longitude of Falmouth, 
which differed about four seconds of time from that which had been 
