Clock. Ixiii 



Observatory are in the meridian and prime vertical, and the points of the compass, 

 reckoning from each corner as a centre, are marked upon the paling surrounding 

 the Observatoi-y ; the observer, therefore, sees at once the direction of motion of the 

 cloud on the paling ; when a portion of cloud cannot be seen which has passed, or is 

 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, ai-e 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 Howard, with certain 

 combinations, which are, in general, sufficiently descriptive. 



104. After June 30, 1844, full sunshine is indicated in the column of meteoro- 

 logical remarks by the symbol O ; when the sun shone through a cloud so as to pro- 

 ject a distinct shadow, it is indicated by the symbol 6 ; when the cloud was very 

 thin, this was 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. 



] 05. The heaviness of the rain falling at the time of observation has been esti- 

 mated after May 10*, 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. 



106. The mean time clock is by Dent of London ; it is kept at Gdttingen 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. 



Description of the Tables of Observations. 



107. Hourly Observations of Magnetmneters, pages 1-69. 



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

 ing, of the observations of the declination magnetometer. Gottengen 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 



