SURVEY OF MASSACHUSETTS. 57 
places but three, have been quite numerous; and of these three, it is believed a sufficient 
number was made for denoting their situations; they are not situate within the limits of 
the state, but so near that it is probable they will be comprehended by the map. 
For the determination of the longitude of the State House in Boston, use was made of 
the observations there or in its vicinity, on every recent eclipse of the sun or occultation 
of a star, on which a corresponding observation was made, in some place in Europe. 
But, as usual, they were very few. It is believed that the only occultations seen there 
and in Europe, within several years past, were those of a Tauri in 1829 and 1830, and 
the only eclipse of the sun that of May 15th, 1836. From these three corresponding 
observations, I was able to deduce the errors of the lunar tables, and thus obtain for the 
longitude of the State House a quantity, less by only a tenth of a second, than that 
deduced by Doctor Bowditch in 1812, from six other observations, made between the 
years 1743 and 1807, which longitude he considered better ascertained than that of any 
other place in the United States. 
The determination of the differences of the longitudes of the other twenty-six places, 
and of the State House, by observations, or the explosion of gunpowder or of rockets, on 
the summits of some of our highest hills, was reluctantly abandoned. As before observed, 
this method is not only very simple and accurate, but probably requires less time than 
any other; but it could not be adopted without the assistance of at least two persons well 
versed in practical astronomy, and it will be recollected that I have not had, at any time, 
the services of even one assistant. 
The method, the last of those above enumerated, was therefore employed; namely, 
that of transporting the time of one place to another by chronometers; and, with a few 
exceptions, all the results stated in the following tables were in this manner obtained. 
In order to diminish as much as possible the probability of error, from any injury that 
might be sustained by the timekeepers whilst undergoing transportation, or from the 
local time at any place of observation not having been precisely ascertained, several of 
these instruments were generally used, (and even they were rarely depended on for a 
longer interval than twenty-four hours, and never for more than two days,) and the com- 
parisons between the places in question were repeated again and again, until a result was 
obtained apparently deserving of confidence. ‘Thus, on referring to the following table, 
it will be seen that the longitude of the First Congregational Church in Northampton 
was ascertained by seventy-four chronometers and twenty-four comparisons with the State 
House, or the Antiquarian Hall, in Worcester; that the longitude of the new Court House 
in Barnstable was ascertained by fifty-nine chronometers and seventeen comparisons, &0., 
&e. And it will be, moreover, noticed, that the difference between the greatest and least 
longitudes of any place thus determined was seldom equal to two seconds of time. 
The local time at any place was ascertained, not by a transit instrument, but by an 
artificial horizon of quicksilver, and a reflecting instrument that had been constructed for 
me by the celebrated Troughton. It was usual to measure at least six altitudes of a 
bright star in the east, and directly as many of another star in the west, or the reverse. 
As it was but seldom that the errors of the chronometers deduced from the two sets of 
altitudes differed two-thirds of a second, and as the mean of these errors was used, there 
is every reason to suppose that the local time was thus well ascertained. 
VOL. Ix.—18 
