ATM 



the equator is 84, and that of the pole 31. 

 priuciplcs the foilowiiig tablp was calculated.. 



TABLE of the Mean Anntial Temperature of the Staiulard 

 Situation in every Latitude. 



Tn forming this table, Mr. Kirwan fought for a (landard 

 fituation, with whofe temperature, in every latitude, we 

 may compare and appreciate the temperature of all other 

 fituations in the fame latitudes, on water only. Accord- 

 ingly, he chofe th.it fituation for a llandard, which is moll 

 free from any bcfiJe the moll permanent caufes of alteration, 

 viz. that part of the Atlantic that lies between the 80th 

 degree of northern, and the 45th degree of fouthern lati- 

 tude, and extending wellward as far as the gult ftreani, and 

 to within a few leagues of the coaft of America ; and all 

 that part of the Pacific ocean, reaching from N.jat. 45' to 

 S. lat. 40" from the 20th to the 275th degree of longitude, 

 call from London, which is by far the greater part of the 

 furfacc of the globe. Within this fpacc the mean annual 

 temperature is as exprefled-in the tabid; and the author has 

 added the temperature of latitudes beyond So'^ in the nor- 

 thern hemifphere, though not ftriftly within the llan- 

 dard. 



Mr. Kirwan has alfo attempted to afcertain the mean 

 monthly tempeiature of the :landard ocean. With this 

 Yiew he i^atcs, that in every latitude, the mean temperature 

 .of the month of April feems to approach very nearly to the 

 mean annual heat of that latitude ; and as far as heat de- 

 .ptrhds on the atlion of the folar rays, the mean heat of 

 every month is as the mean altitude of the fun, or rathtr, 

 as the fine of the fun's mean altitude during that month. 

 Hence to find the mean heat of May, fay, as tlie fine of 

 the fun's mean altitude in April is to the mean heat of April, 

 fo is the fine of the fun's mean altitude in May to the mean 



A T I\I 



Upon thefc heat of May. By a fimilar procefs, the temperatures oF 

 Juno, July, and Auguft may be found ; but tins rule would 

 give the temptraturcs of the fucceeding months too low ;:. 

 becaufe it dots not comprehend the quantity of heat accruing 

 to the atinofphere by communication of the internal heat of 

 the globe, wliich in every latitude is nearly the fame as the 

 mean annual heat of that. latitude. Kence the real tempe- 

 rature of thefe m.onths muft be i-cgarded as an arithmetical 

 mean between the aftronomical and .terrellrial heats. E. g. 

 In lat. 51^, the aftronomical heat of the month of Septem- 

 ber 1^44.66^, and the mean annual heat is 52.4° ; coni'e- 



44.6-}- 52.4 

 quently the real heat of this month is = 48.4,. 



which is more conformable to obfervation. Mr. Kirwan has 

 with great labour formed a table, fliewing the monthly mean 

 temperature of the ftandard ocean from lat. 80" to lat. lo*^. 

 Hence he Ihews, that the coldell weather in all climates 

 prevails in the month of January ; and that July is the 

 warmtfl: month in all latitiides above 48°; but in lower lati- 

 tudes, Auguft is generally the warrnelt ; that .Oeceniber and 

 January, and alio June and July, differ but little ; that 

 the diflerences between the hotteft and coldeft irionths, with- 

 in 20° of the equator, are incoiifiderable, and that tlK'y in- 

 creafe as we recede from the equator ; that in the hlghefl: 

 latitudes we often meet with a heat of 75 or 80 degrees f 

 that every habitable latitude enjoys for two months a heat of 

 60 degrees at leaft, which feem.s to be uecefTary for the 

 growth and maturity of corn ; and that the quiclinefs of ve- 

 getation in the higher latitudes proceeds from the duration 

 of the fun above the horizon ; that as the cold of the higher 

 latitudes, and the heat of the lovi'er, are moderated by the 

 vicinity of fess and mountains, thefe, iullead of being irre- 

 gular and fortuitous, may be regarded as a wife and benefi- 

 cial provifion of nature, in this refpetl as well as in many 

 others. Mr. Kirwan lias alfo lliewn, that the greateil cold 

 within the twenty-four hours generally happens half an hour 

 before fun-rife, in all latitudes : the greattd heat in all lati- 

 tudes between 60° and 45° is found about half paft two 

 o'clock in the afternoon ; between lat. 45" and 35°, at two 

 o'clock. ; between lat. 35"^ and 25°, at half pall one ; and 

 between lat 25° and tlie equator, at one o'clock. On fea, 

 the difference between the heat of day and night is not fo 

 great as on land, particularly in low latitudes. 



TABLE exhibiting a Comparifon of the Temperature of 

 London, with that of other noted Places, 



The firft column of this table exhibits the differences of 

 the annual temperature ; the fecond, that of Januar)- ; and 

 the third that of July ; that o£ Loudon, as the llandard, 



bsin^ 



