91 
An accident to one of the micrometer-screws of the circle, 
rendering the simultaneous labor of both assistants necessary 
at the zones, their duties were fixed for each alternate night, 
while Gilliss himself employed the intermediate ones in ex- 
amining such of LaCaille’s stars between the zenith and the 
pole, as had never been twice observed. The pages of the 
astronomical periodicals of that time bear witness to the 
effectiveness of his scrutiny, by the record of many hundred 
 errors'detected in the Catalogue of LaCaille. On the recep- 
tion in June of new micrometer-screws from the makers in 
’ Berlin, the original system of observations was resumed. 
During the series of observations of Venus, Gilliss records 
several occasions when the cusps of Venus could be distin- 
guished by the unassisted eye. 
I will not dwell further upon the details of the observa- 
tions, for they are fully described in the magnificent volumes 
containing the results of the expedition. Let me simply 
sum up the work accomplished. Between the 6th Decem- 
ber, 1849, and the 13th September, 1852, series of micro- 
matic comparisons of Mars were made in forty-six days 
during the first, and ninety-three days during the second op- 
position, and micrometric comparisons of Venus on fifty-one 
days during the first, and twenty-seven days during the second 
inferior conjunctions ; the observations on each day being con- 
tinued through several hours, whenever the sky permitted, 
and the work being executed with the same delicacy and care 
which had characterized those earlier transit-observations on 
Capitol Hill in this city. In addition to this, very much 
else had been done; but these grand series of observations, 
executed in precise conformity to the programme laid down, 
warranted the confidence that his devotion had not been in 
Vain, and that the problem of the parallax would be solved. 
His two hundred and seventeen series of observations ex- 
