Sen 
SURVEY OF MASSACHUSETTS, 41 
able to form a correct opinion of the condition of the atmosphere, favourable for viewing 
distant objects. 
_ At the latter end of the month of November, 1835, I was at the trigonometrical station 
in Fairhaven endeavouring to measure the angles which were deemed necessary from that 
station. Soon after our arrival, we had a fall of snow which covered the ground several 
inches thick. Severely cold weather succeeded it; and although the atmosphere appeared 
uncommonly transparent to the unassisted eye, still we were unable to see our distant sig- 
nals, particularly those upon Martha’s Vineyard, and the Elizabeth Islands. The line of 
sight to these signals lay across the waters of Buzzard’s Bay, and the Vineyard Sound. 
In a few days after the snow had fallen, the weather became warmer, and a rain ensued, 
which took off nearly all the snow. On the morning following the rain, namely, the fifth 
of December, we went early to the station, and discovered that all of our signals could be 
seen with tolerable distinctness, although the atmosphere was apparently not near so 
transparent as it had been at several of our previous visits to the station. The heavens 
were densely clouded. I think the sun did not appear at all, or if seen it must have 
been so very dimly as not to have perceptible influence upon the atmosphere. ‘The day 
of course was, comparatively speaking, a dark one. 
We commenced our operations of measuring angles as rapidly as we could; but we had 
not been long engaged in our work before the atmosphere began to presenta very curdled 
appearance, and our signals to appear dim. Ina short time they appeared plainer again, 
and then again more dim: the appearances thus alternating. Having a thermometer at 
hand, I directed Mr. Read, one of my assistants, to observe that instrument, and see if 
any changes took place in it corresponding with the changes in the appearance of the 
signals; and we soon ascertained that these changes always occurred together. ‘The day 
was a very remarkable one for our operations, which we were enabled to prosecute with- 
out intermission until we had completed all we desired at the stations; and from the time 
we first commenced observing the thermometer until our work had ended, a slight change 
of the instrument could be easily detected from the appearance of the signals, particularly 
when looking across water. I think the change of appearance was not so strikingly appa- 
rent across the land. Having made these observations, I endeavoured to estimate the 
temperature of the surface of the land and water across which our observations were made, 
The sun not having shone at all, or at most not sufficiently bright to have any perceptible 
effect during the time of our observations, the surface of the earth might be considered 
of a uniform temperature. It was frozen, and the preceding night had been warm and 
rainy; and I therefore concluded that the surface of the earth must be at or near a freezing 
temperature, namely, 32° of Fah. ‘The water, of course, must have been several degrees 
warmer. Still it was very cold; for a few days previous, we had had a considerable fall 
of snow, which, as is well known, chills water very rapidly. ‘The weather which succeeded 
the snow storm had been extremely cold. I did not make any memoranda at the time, or 
if I did I cannot now find them, but I presume the thermometer must have stood as low 
as 10° or 12°, until within twelve or fifteen hours before the observations were made. 
The waters of Buzzard’s Bay and the Vineyard Sound are very shallow, and ebb and 
flow very little; of course the waters could receive but a slight influence from the warm 
VOL. IX.—14 
