Royal Society. 377 



Details are given in the commencement of the paper showing the 

 care bestowed on the examination of the thermometer employed, 

 with a standard divided " cl Vechelle arhitraire," by the method of 

 M. Regnault; as well as the precautions adopted for its fair ex- 

 posure, and for its protection from rain and radiation. The obser- 

 vations were made by the non-commissioned officers of the detach- 

 ment of the Royal Artillery employed in the duties of the obser- 

 vatory. 



The period of twelve years comprises two series, in one of which the 

 thermometer was observed hourly, and in the other less frequently, 

 each observation ki the second series receiving however a correction 

 to the mean temperature of the day furnished for every hour and 

 every day of the year by the first series. The two series, each of 

 six years, are separately discussed ; from the first series equations 

 are derived from the mean monthly temperatures by the method 

 suggested by Bessel (Astron. Nach. No. 136), whereby the most 

 probable values of the temperature, on every day and every hour, 

 are computed corresponding to the whole body of the observations. 

 These the author regards as approximate normal values, and by 

 comparing with them the actual daily temperatures, — which in the 

 first six years are the means on each day of twenty-four equidistant 

 observations, and in the second six years the means of all the obser- 

 vations made on each day, each observation having been corrected 

 for the hour in the manner described, — the non- periodic variations 

 for every day in the year are obtained and are given in a table. 



From the approximate normal temperatures the author has repre- 

 sented in a Plate the phenomena of the temperature at Toronto, ac- 

 cording to a method which, if applied to the different meteorological 

 elements and in different localities, might, he thinks, materially facili- 

 tate their intercomparison. This method, in which three variables are 

 represented, one being dependent on the other two, is essentially the 

 same that has been long used in magnetic maps, and in the ordinary 

 isothermal maps ; from which latter however it differs in this respect, 

 that, whereas in the ordinary isothermal maps the two variables on 

 which the variation of temperature is dependent are the geographical 

 latitude and longitude, in the present case the two variables are the 

 hour of the day and the day of the year. The variation of tempe- 

 rature is here referred therefore to time and not to space ; a distinc- 

 tion which the author proposes to convey by employing the term 

 Chrono-Isothermals, as applicable to lines of this description. From 

 the delineation in the Plate, and from the tables contained in the 

 paper, many characteristic and some peculiar features of the climate 

 and meteorology of the part of the North American Continent in 

 which Toronto is situated, are readily perceivable. Several instances 

 are pointed out ; amongst these may be noticed the peculiar ano- 

 maly of the North American winter, which is very conspicuous in 

 the Plate ; and the absolute as well as relative variability of the tem- 

 perature at different seasons of the year, exhibited by means of a 

 numerical index analogous to the probable error of the arithmetical 

 mean of a number of partial results, and deduced in a similar man- 

 ner from the differences of individual years, months, and days, from 

 Phil, Mag, S. 4. Vol. 5. No. 33. May 1853. 2 C 



