230 Translation fromthe Astronomical Jour. of Hamburgh. 
ever Mr. H. says, that even without the direct light of the 
sun, they also rendered good service, and were visible at 
great distances.* 
Mr. H. has also communicated his metheds for the com- 
parison of the standard ena of length, and the results 
of their application ; we gain by this a new comparison o 
the French and Englis seocnanaleds which I shall quote more 
in particular. There were three meters present. One 0 
iron, which was one of those made the committee of 
weights and measures in Paris 1799, and distributed as au- 
thentic among the foreign deputies; the two others, the one 
brass, the other iron, were of Lenoir, but not compared 
rectly with the original, they therefore were not sohacened 
as principal in the results of comparison. These meters 
were compared with a scale of Troughton, of eighty two 
inches in length, diviciad upon silver to tenths of inches, to 
which is added, a micrometric apparatus to take off measures 
from the scale. Instead of the usual method in comparing 
a meter a bouts with one 4 traits, to place butting pieces with 
lines drawn near to the end of them, the distances of which, 
the same thickness as the meters, and obtained, by the 
juxtaposition of both, a line, aes presented itself like : 
division line of the scale. By means of several experiments, 
(reduced to 32° Fah. and sidsoting the expansion of the 
iron and the brass, as Mr. H. determined it by his own exper- 
iments, namely between the point of melting ice and the 
boiling heat of water ;) 
* To use the heliotrope, two con the attendance of 
an assistant at each signal station ages to roe ~omoatl and its actual il- 
jumination by the rays of thesun. Had Mr. Hassler’s opera ration been intended 
to include no more than a net work of great triangles, the heliotrope might tee 
more we hoe ti d have been observed 
But the survey being necoesarity co noe - with a view to its eenaiiets 3 a 
yarograph ichal panedies ve been ne- 
cessary ery the signals to elses 3 it basen as Cy 
sible to employ so many separate attendants. Mr. Hassler’s si also answer 
well even ina cloudy state of the atmosphere, if the other iy i geaterce be 
ve frequently happens. The objection that two signals could rarely 
have shewn an an equally well defined image of the sn, doos not hold eo 
