326 Instructions for Making and Registerijig 



vation at each station should commence at 6 o'clock a.m. of 

 the appointed days, and terminate at C o'clock p.m. of the 

 days following, according to the lisiial reckoning of time at the 

 place. During this interval, the Barometer and Thermometer 

 .should be read off and registered hourly, or at all events, at 

 intervals not more than two hours asunder, and the precise 

 hour a'if/ »2/?ij//e of each reading should be especially noted. 

 For obvious reasons however, the commencement of every 

 hour should, if practicable, be chosen, and every such series of 

 observations should be accompanied by a notice of the means 

 used to obtain the time, and wlten practicable, by some obser- 

 vation of an astronomical nature, by which the time can be 

 independently ascertained within a minute or two.* As there 

 is scarcely any class of observations by which meteorology can 

 be more extensively and essentially promoted, it is hoped that 

 not only at every station of importance in this colony but over 

 the v,-hole world, and on board ships in every part of the ocean, 

 individuals will be found to co-operate in this inquiry. Every 

 communication of such observations addressed by channels as 

 secure and as little expensive as possible to the Secretary of 

 this Institution, will be considered as highly valuable. 



»' 



III. Of Meteorological Instruments, and first of the 

 Barometer and its attached Thermometer. 



The Barometer is the most nnportant of all Meteorological 

 instruments. Its office is to measure the actual pressure of 

 the atmosphere on a given horizontal surface at the time and 

 place of observation. Its fluctuations are observed to have 

 considerable relation to changes in the weather, and especially 

 of the wind. Hence its use as a weather glass. 



A Barometer should be exam.ined, before setting it up, for 

 air-bubbles in the tube, and for the existence of air above the 

 mercury in the upper part of the tube. This is done by gently 

 inclining the instrument either way from the horizontal position 

 a little up and down^ when air-bubbles, if large, will be seen 

 to run to and fro, an<l m.ust be evacuated by inverting the 

 instrument and by gentle blows on it with the hand, driving 

 them up into the cistern. If this cannot be done, the instru- 

 ment is useless. If air exists to an objectionable amount nlx^ve 

 the quicksilver, it will not tap sharp against the upper end of 

 the tube when the barometer is quickly inclined from a vertical 



• Forosam|ile, the first appcarancea and last disappearances of the' 

 Sim's upper and lower border, above and below the sei horison, if a' s a 

 or on the coast,— or, on land lh*» exact length of the shadow o( a vertical 

 orbjcct of determinate length on an liorizontal l»v-l, at a precise roonipnt 

 pf tim" 'not ton near noon), Vc. 



