74 ALLISON — ON METEOROLOGY. 



Art. IX. Notes on the Weather at Halifax, N. S., 



DURIJv^G THE YeAR 1867. By FREDERICK AlLISON. 



In this, the first paper which I have the honour to read be- 

 fore this Institute, I have endeavoured to keep close to a review 

 of 1867, without exploring bye-paths leading to subjects which 

 might tempt one beyond ordiuaiy limit — subjects requiring wzore 

 full treatment than I could sfive them to-nio'ht. 



The plan followed in observing the several features of the 

 weather, described below, has been this. Cloud is classed by 

 figures from to 10, the former being a perfectly clear sky, the 

 latter complete cloud. The intermediate numbers being so 

 many tenths of the sky obscured. The mean temperature of 

 each day is calculated from 12 observations, read from a 

 Negretti and Zambra Thermometer, placed five feet from the 

 ground, wath a N. N. W. aspect, and always in the shade. This 

 thermometer has been satisfactorily tested in water just at the 

 point of freezing, and is frequently compared, to ensure its con- 

 tinued correctness, with two other thermometers similarly tested ; 

 and which, under the same conditions, mark alike. The 12 

 observations are read directl}^ from the thermometer, except 

 those at 2 a.m. and 4 a. m. ; which, with the aid of the Minimum 

 Register, and the midnight and 6 a. m. readings, can safely be 

 set down at an estimated point so as to be taken into the calcu- 

 lation of the Mean. Some observers do, for convenience sake, 

 take observations at 7 a. m., 2 p. m. and 9 p. m. only, and cal- 

 culate the mean from these, which give, on ordinary days, a very 

 close approximation to a more elaborate calculation. But it is 

 evident that on days with abnormal changes of temperature this 

 plan runs a great risk of being erroneous. The minimum of the 

 24 hours is read from a Negretti and Zambra Thermometer, 

 with self-acting Register in spirit, placed as above mentioned. 

 The Maximum read in the usual way. During the year innne- 

 diately under consideration this evening, I could only mark the 

 number of hours of rain ; now, through a friend's kindness, T 

 have an accurate rain guage, of the simplest, and, as I believe, 

 the best kind. Wind is noted, as cloud also, at 7 a.m., 3 p.m. 

 and 11 p. m. The direction of wind is taken from an ordinary 

 yane, but the force I have to estimate from observation and 



