Clock, &c. Ixi 



about to pass, through the zenith, it is generally easy to determine very nearly the 

 vanishing point of the motion of any portion of cloud, by watching its progress for a 

 short period ; there can be no hesitation in saying, that the motions of the upper 

 currents of air thus observed, are better determined than the motion of the lower 

 or surface current observed from the vane. The directions of motion of the clouds 

 in three strata (scud, including cumuli ; cirro-stratus, including cirro-cumuli ; and 

 cirri), are given in numbers of points of the compass, reckoning N = 0, E = 8, 

 S = 16, W = 24. The nomenclature adopted is that of Mr Howaed, with certain 

 combinations, which are, in general, sufficiently descriptive. 



104. Full sunshine is indicated in the column of meteorological remarks by the 

 symbol O ; when the sun shone through a cloud so as to project a distinct shadow, 

 it is indicated by the symbol 9 ; when the cloud was very thin, this is indicated 

 occasionally by the symbol O ; and when the sun's disc only was visible, the symbol 

 • is used ; similar symbols are used for the moon. The heaviness of the rain fall- 

 insf at the time of observation has been estimated, and is noted in the column of 

 meteorological remarks, upon the supposition that the heaviest fall is 10 : thus, 

 rain^ is rather heavy rain; rain^, is the heaviest observed in 1844; rain**"^, is just 

 perceptible ; and rain""^, is a light, spitting, Scotch mist. 



Clock, &c. 



105. The mean time clock is by Dent of London; it is kept at Gbttingen mean 

 time by comparisons with the transit clocks in the Astronomical Observatory, the 

 errors of which are determined by Sir Thomas Brisbane, by myself, or by Mr 

 Welsh. The rate of the clock is kept small. 



106. A fire-place was formed in the space marked F (Plate I.), in October 

 1845, the east anteroom being employed afterwards as a computing room ; the 

 chimney was formed of fire-brick tubing (which it was found could not appreciably 

 affect the positions of the magnets), the grate and &re-irons were of copper. 



Description of the Tables of Observations. 



107. Hourly and Daily Observations of Magnetometers, 1845 and 1846, pages 

 1-68 and 288-323. 



The first column contains the Gdttingen mean solar time, astronomical reckon- 

 ing, of the observations of the declination magnetometer. Gdttingen time is 49™ 50' 

 in advance of Makerstoun time. The second column gives the absolute westerly 

 declination in degrees, minutes, and decimals of a minute, deduced as described. 

 No. 17. 



The third column contains the observations of the bifilar magnetometer in scale 

 divisions, corrected for temperature to 26° Fahr. (see Nos. 69 and 73) ; increasing 

 numbers indicate increasing force. The bifilar is observed 2™ after the declination. 



MAG. AND MET. OBS. 1845 AND 1846. Q 



