488 Royal Society. 
He, however, throws it out as a conjecture, that this latter action 
may be the result of an unusual degree of vital contractility, residing 
either in the cellular tissue. or in the minute blood-vessels of the 
iris. It is from elasticity, he believes, that the iris derives its power 
of accommodation to changes of size, and its tendency to return to 
its natural state from extremes, either of dilatation or of contraction ; 
but beyond this, elasticity is not concerned in. its movements. 
Feb. 16.—The following papers were read, viz.— 
1. “ Tide-Observations at Tahiti:” by Captain Edward Belcher, 
R.N. Communicated by Captain Beaufort, R.N., F.R.S., &e. 
This paper consists of copies of the Tide Journal, registered at 
the Island of Motuatu, in the Harbour of Papeete, and of a short 
comparative series made at Point Venus. ‘They were conducted by 
Mr. M°Kinley Richardson, Mate. The construction of the tide- 
gauge is described; and an account is given of the methods of ob- 
servation, and of the precautions adopted to ensure accuracy. The 
results are specified in the following letter from the author to Cap- 
tain Beaufort, which accompanies the paper :-— 
“‘ Her Majesty’s Ship Sulphur, Woolwich, August 2, 1842. 
“ Sir,—Referring to the Tide Registries, forwarded on my arri- 
val, I beg leave to offer the following general remarks upon the 
tides at Tahiti. 
“In consequence of your very special instructions relative to the 
determination of the actual periods of high water at the Island of 
Tahiti, the most minute attention was paid to this subject; and as 
these periods could only be approximated, recourse was had to my 
old method (successfully practised in the Lancashire survey), of de- 
riving them from the Equal-altitude system. 
“ By a reference to the Tide Registry annexed, it will be found 
that there are two distinct periods of high water, during each interval 
of twenty-four hours; and that during the seven days preceding, 
and seven days following the full and change, they are confined be- 
tween the limits of 10 a.m. and 2" 30™ p.m., the whole range of 
interval, by day as well as by night, being about 4 27™. 
«“ Commencing with the seventh day preceding the full moon, viz. 
the 9th of April, it will be perceived that high water occurs at 
10 a.o., this being the greatest A.M. interval from noon; and that 
on the 16th, at the full moon, it occurs nearly at noon. 
* Passing on to the 23rd, it reaches the greatest p.m. limit at 
25 30™, and on the 2nd of May again reaches the noon period. 
“ Between the 23rd and 24th, however, a sudden anomaly presents 
itself. Throughout the day of the 23rd, the variation of the level 
does not exceed 23 inches, and the general motion is observed to be 
‘irregular.’ The time of high water is also the extreme p.m. limit. 
“ On the 24th we discover that it has suddenly resumed the most 
distant A.M. period, viz. 10 A.M., but proceeds regularly to the noon 
period at the change. 
“ Although the differences of level do not at full and change ex- 
ceed 1 foot 44 inches, still I presume that we have sufficient data 
to establish the fact,—that it is not invariably high water at noon 
