52 Effect of the Pressure of the Atmosphere on the Ocean. 
understood the Indian method, according to which it was devel- 
oped. Hutton observes that he had seen a book printed in Ger- 
many in which rules for operating with each measure to twelve 
was given, but does not intimate that he or the author regarded 
it as a development of the several measures of one scheme, but 
seems to consider it, as mathematicians in general appear to do, as 
so many independent methods. Could the several schemes, and 
especially the Indian, be properly developed in all their different 
measures, the subject of numbers would assume a more general 
aspect. 
Middlebury, Vt, September, 1845. 
Art. 1X.—On the Effect of the Pressure of the Atmosphere on 
the Mean Level of the Ocean; by Captain Sir James Cuark 
Ross, R.N., F.R.S.* 
Tue author states that, in September, 1848, Her Majesty’s ship 
Enterprise and Investigator having anchored in the harbor of Port 
Leopold in lat. 74° N. and lon. 91° W., a heavy pack of ice was 
driven down upon and completely closed the harbor’s mouth, thus 
effectually preventing their egress, and compelling them there to 
pass the winter of 1848-49, It was during that period that the 
series of observations here presented to the Royal Society was 
obtained; and, as the observations were made under peculiarly 
favorable circumstances, the author considers they will throw 
ight on. the movements of the tides, and on some of the 
causes of their apparent irregularities. 
Soon after the harbor had been completely frozen over, a very 
heavy pressure from the main pack forced the newly-formed sheet 
of ice, which covered the bay, far up towards its head, carrying 
the ships with it into such shallow water that at low spring-tides 
their keels sometimes rested on the ground. Under these circum- 
stances the movements of the tides became to the author an object 
of great anxiety, and consequently of careful observation, in order 
to ascertain the amount of irregularities to which they were liable 
in that particular locality. 
The first few days’ observations evinced much larger differen- 
ces in the elevation or depression of successive high or low-waters 
than could be accounted for by any of the generally received 
causes of disturbance ; and the author was at once led to connect 
them with changes of the pressure of the atmosphere, from per- 
ceiving that on the days of great atmospheric pressure high-water 
was not so high as it ought to have been, and low-water was 
lower than its proper height ; and that the reverse took place on 
days of smaller pressure. 
ny gs Roy. Soe. Lond, June, 1854; Lond, Edin, and Dub. Phil. Mag,, Oct. 1854, 
