142 Report of Observations on the Transit of Mercury. 
machine. The nature of this last improvement will be hereafter 
explained. The gun, the rotary engine, and some other modifi-_ 
cations, will be hereafter described. 'The above modifications of 
the engine, the rotary form and the other instruments, were all 
invented in less than a month’s time after the single axial engine 
and communicated in confidence to a few friends. 7 
Washington, D. C., June 10, 1845. 
Arr. XVI.—Report of Observations on the Transit of Mercury, 
May 8th, 1845; by Professor Otmsrep, of Yale College. 
By recurring to the records of observations on previous transits 
of Mercury, as given in the Philosophical and Astronomical 
Transactions, and in various scientific journals, we find that the 
circumstances under which they have occurred, have seldom been 
entirely favorable. Hither the ingress or the egress has happened 
in the night ; or one or more of the contacts, and frequently all, 
have been concealed by clouds. Of the several transits which 
have taken place within the present century, the late transit was 
the only one which presented itself to our astronomers under cir- 
cumstances favorable to observation. Fortunately, this tran- 
sit afforded toa number of accurate observers an unobstructed 
view of the entire phenomenon, and to others, the opportu- 
nity for accurate observations on at least one set of contacts, 
either those of the beginning or those of the end. Presenting 
itself to all parts of the United States, as far west as New 
Orleans, between the hours of ten in the morning and six in 
the evening, and consequently ata period in the twenty-four 
hours extremely convenient to the astronomer, it afforded’ t 
best opportunities for determining the times of contact, and all 
the physical peculiarities of the phenomenon. In some parts of 
the country, on the east, indeed, the morning was threatening 
and boisterous, so as to prevent good observations on the ingress; 
and in other parts, on the west, clouds prevented observations on 
the egress; butso far as we have heard, all observers enjoyed the 
satisfaction of seeing at least either the ingress or the egress. At 
New Haven, New York, West Point, Philadelphia, Cincinnati 
and Charleston, the sky was cloudless throughout ; at New Ha- 
ven the covering of clouds, which had overspread the morning 
