992 



additional support necessary for the joists when the extraordinary- 

 weight of the instrument is transferred to the receiving carriage, 

 has rendered impracticable the adjustment of our microscopes thus 

 far. But I hope to have the instrument fully at work by the 25th, 

 stays having been driven in beneath the joists. A more exquisitely 

 finished instrument was never turned out of a workshop. 



Immediately after our location, meteorological observations were 

 commenced, embracing eight periods of the day, at equal intervals, 

 viz. at 3, 6, 9, 12 a.m. and p.m. Nothing is so striking to the 

 stranger as the great dryness of the atmosphere and its almost perfect 

 transparency, the ordinary difference of the dry and wet thermome- 

 ters being above 12°, and, except over the Cordilleras to the N.E., 

 clouds being rarely seen at this season of the year. Our barometer 

 is of Mr. Hassler's form of construction, with a capacity above 0*6 in. 

 Taking from the volume containing astronomical observations (no 

 other being at hand), the means between 9 p.m. and meridian for 

 the last twenty-one days of December, they are 28*126 in. ; air 70°*3 ; 

 wet 57°*8 ; and fluctuations during the same period respectively, 

 28-247 in. to 28*023 in.; 74°-4 to 65°-6 ; 61°-9 to 51°-3. From 

 10 A.M. till noon is the warmest period of the day; then a breeze 

 sets in from S.W., which moderates the fierceness of the sun's rays 

 until he sets. Our vicinity to the snow on the Cordilleras, N.E. from 

 the city, renders night always pleasant, and indeed the temperature 

 is never oppressive when not exposed to the direct action of the sun. 



On unpacking the magnetical instruments, no top could be found 

 for one set of the legs sent by Mr. Jones, and as it would be 

 next to impossible to have a triangle made for securing them to- 

 gether, much time is unavoidably lost. One of the 3*67 in. mag- 

 nets, too, is so greatly oxidized, I shall not use it until I hear from 

 you again ; and as there are no tidings of the altitude and azimuth 

 instrument, the declinometer also must remain in its case. The hill 

 on which the observatories have been erected being very decidedly 

 polar, our observations for the horizontal force and dip have been 

 made in a vineyard a few hundred yards to the eastward, and where 

 we shall continue to make them for the present. Our own residence 

 would have been greatly preferable ; but the two portions being only 

 about 16 feet square each, and having windows on at least two 

 sides protected by stout bars of iron, it has been deemed objection- 

 able. When the winter comes on it is probable a small abode house 

 will be put up for them ; at present we use them in the open air. 

 The periods assigned for observation are, the 1st, 11th, £ind term," 

 day of each month, commencing about 11 a.m. and ending about 

 4 P.M. This is all which my force will permit me to do ; but if 

 we can obtain means to mount the other tripod stand, so as to avoid 

 loss of time in the vibration experiments, we shall have abundant 

 leisure for the vertical and total forces as you suggest. Were the 

 brass rings for determining the magnetic moments of the deflecting 

 magnets measured and weighed by Mr. Jones? I have made out 

 No. 12j outer diameter, 3*025 in. ; inner, 2*338 in. ; weight, 949 troy 

 grains. 



