SS os -F. = 
Wood’s Portable Self-Registering Tide-Gauge. 71 
This operation seems to be reversed in the case of the Mediterranean 
sea, if, indeed, the inward current at the Straits of Gibraltar has any 
relation to the superior saltness of that sea. An under-current mov- 
ing outward, would, in that case, be the natural result. 
Tf an inland sea should undergo a change in its specific gravity, 
owing to alterations of temperature, or in the proportion of its 
saline contents, its level would also be changed ; and, therefore, 
these considerations should not be overlooked in investigations of the 
comparative heights of sea and land, at different periods. 
It is, perhaps, worth inquiring, how far the low level of the Cas- 
pian Sea may be due to the high specific gravity of its water, which 
is said to be very saline, and very deep, and its mean temperature 
is probably low. —The Eleventh Annual Report of the Royal Poly- 
technic Society. 
Mie us) Se eee 
Account of a Cheap and Portable Self-Registering Tide-Gauge, 
invented by JouN Woob, Esq. of Port-Glasgow, and which 
has been two years in use. With examples of the work 
done by it. By Joun ScoTr Rossbuu, Esq., F.R.S.E., 
F.R.S.8.4. Communicated by the Royal Scottish Society 
of Arts.* With a Plate. 
In the course of the tide researches in which I have for some 
time been engaged, I have continually felt the want of a 
simple, cheap, and portable machine for registering tidal 
phenomena; such a one as might be erected and applied, 
either temporarily or permanently, without requiring much or 
close attention in its use, or nice adjustment for its operation. 
If this were attained, I have felt confident that few harbours 
of importance would be without a tide-gauge. This is of the 
greater importance, owing to the present position and aspect 
of our knowledge of the phenomena of the tides ; observations, 
continuous, simultaneous, and of considerable period, being 
all that is necessary to afford us the means of placing this 
complicated subject in a highly respectable position among 
the accurate sciences. 
Ups oh es Ae Se 
* Read before the Royal Scottish Society of Arts, Feb. 12. 1844, and 
the Silver Medal, value Seven Sovereigns, awarded to Mr Woop, 11th 
November 1844. 
