METEOROLOGY. 



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case, rather as accidental, than as affording any satis. 

 factory evidence of the accuracy of the formula. The 

 observations were made by Mr. Play fair three times a 

 day, viz. at eight in the morning, one or two in the 

 afternoon, and ten at night. Now, though it is im- 

 possible, from the well-known character of that emi- 

 nent philosopher, to doubt the accuracy of Mr. Play- 

 fair'* observations, still it ia an assumption which is yet 

 to be proved, that the mean temperature of t he-c hours 

 is the true mean temperature of the day ; and even if 

 this were proved, the error of half a degree is much 

 too great to admit the application which has been made 

 of the formula. According to our own observations, 

 the mean temperature comes out considerably lower 

 thantli.it given by the rule, so that the difference seems 

 in all cases to be on the same side, at least in latitudes 

 above 41. At Kinfaun Castle, the seat of the Right 

 Lord Gray, latitude 56 24', tl>e mean of the 

 daily extreme*, for six years, from 18(3 to 1818 inclu- 

 sive, is 46*. 3 ; and making allowance for the elevation 

 of the place, (ISO feet) 46 7. By Mayer's formula, it 

 ought to be 47.7, and by Leslie's 48. 1 . The mean tem- 

 perature of another place, under the same latitude, luit 

 more elevated and less sheltered, deduced from the 

 daily extremes for five year*, from 1814 to 1818, ia 

 45". 7, and making allowance for the elevation 46". 2, 

 which differs >till more than the former from the re- 

 sult of the formula 



Another method, and perhaps the most correct of 

 any, of determining the mean temperature of any 

 given latitude, i- by observing copioiu and well shad- 

 ed tprings There can be little doubt that the mean 

 temperature <>f the ground must, upon the whole, coin- 

 cide very nearly with that or the atmosphere, from the 

 w II known tendrncy of heat to diffuse itself, so as to 

 establish an equilibrium in temperature between two 

 contiguous bodies. Every fluctuation of heat and cold 

 at the surface will be communicated to the interior, more 

 or lea* quickly according to circumsunce*, till the whole 

 masa acquire* the same temperature, while those fluc- 

 tuation* mutt obviously become IBM sensible in propor- 

 tion to the depth below the surface. VVe are thus led 

 to expect, that beyond a certain depth the temperature 

 become* atationary at or very near the mean tempera 

 ture of the latitude ; and tlie advantage of O(MI 

 the temperature ot a copious spring is, that at all thnu 

 it will give an a proximal ion to t!ii* quantity. At the 

 tame time, howe-t-r, we cannot admit that this import- 

 tant element in meteorology can be determine.) even 

 lij the help of the most copk>u spring, with all the fa- 

 > to cility that ha* of late been supposed. A tingle obser- 

 vation, at any season ot the year has been represented 

 qiwntljr ot luffiVicnt, not only to fix the true mean temperature, 

 but, by a comparison with the standard temperature at 

 the level of the sa, given by the formula stat-d above, 

 to determine with ; -lie elevat. 



an opinion which, besides leading to > rmin < i- < 

 ion in particular cate*, ap(>ear* calculated to retard 

 the general progress) of meteorological sen . 

 the advocate* for this sun. in * y mrt'iod ot o ii 

 mean teir> have produced only one mi.v 



*prini; in wh:ch there i ca 



or diminution ot heat throughout the j .ir, viz. the 

 fount.i'ii of Vaucliue. wl.os* temperature, it ; 

 dot* not vary unt-irnlli of a degree, though, I'-. 

 strangr i i elsewhere Mated, on l/ie 



tame ii*l/.or>ty. Ion* upwards at I if a degrcei. This lut 

 qua .tity, we l>elieve, will be found in ^enernl to l--he 

 i of the (< iet spring", and no <onfi<:, nee 

 therefore can be placed in any conclusion that niaj be 



gy- 



Tnnpcra- 

 lurr of 

 r nc* as 



,,pr..i mi- 

 tton to Ik* 



t::. in* *n 



tempera* 

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157 



drawn from a single observation. Before we can de- SK-teoroio. 

 pend on such an observation, as determining the mean 

 temperature, we must have previously ascertained, 

 either that the spring does not sensibly change from 

 one season to another, or that, at the time of observa- 

 tion, it was at its mean annual temperature. The re- 

 mark applies still more forcibly to the measurement of 

 altitude,. It is well known, and indeed mny be infer- One obser- 

 red, from the very nature of spring*, tiiat the higher vaiion not 

 and more extensive the collecting surfice of a spring, j"^^,. 

 or tlie lower the point at which it iawe*, the more m l ^ llrirg 

 steady will bf its temperature. In proportion, there- , hl . t .| UVB . 

 fore as the spring is elevated, the more liable will it be ,, O f t he 

 to variations, and the greater the necessity of multiply- place. 

 ing olwervations to determine its mean temperature. 

 Nor is this the only circumstance th t nfiocU the accu- 

 racy of the result thu-i obtained. The tem|>erp.tiire of 

 the atmosy' ere, in this climate, is foiiml to diminish in 

 proportion to the height above the level of the sea, at 

 the rate of one degree of Fahrenheit for every !)y rt k 

 of aacent ; so that an error of a single degree in taking 

 the temperature of the "printr, will produce a differ- 

 ence of 270 feet in the altitude ol the pi ice. Mr Les- 

 lie has indeed iv-n one instance, in which the eleva- 

 tion of two points on the name hill, determined in this 

 way, agree* almost exactly with the altitude found by 

 levelling ; but it must be obvious, that a (ingle mine:- 



is kind, which might IK- purely iccidenUl, 

 is not -ufficient lo remove the objections now tated. 

 The Crawley and HI* k spring!, on the ridge of the 

 Penilaml Hills, were examined, and their temperature 

 found lo be 46.2 and 45. These quantities being sub- 

 tracted from 4.S, the standard temperature of the 1 1- 

 .tl the level of the sea, according to Mr Leslie's 

 formula, and the differences multiplied by 270, the pro- 

 duct* are 5I>7 and ft.'M, for the respective heights of the 

 spring-.. The real heights found by levelling were :'<()! 

 This coincidence is no doubt very remark- 

 able ; and there i one point in which it is perfectly sa- 

 tisfactory. The difference of temperature between the 

 two spring* i* l.2, which, multiplied by a 70, gives 



r the elevation of the one above the other. 

 being only (i feet more than the real difference, a* found 

 by I. veiling. So far it illustrate* the law by which a 

 diminution of temperature takes place according to ele- 

 vation ; and had the temperature of the springs t>een 

 compared with that of another equally permanent, at 

 the level ot the sea, we have no ilou'it that the absolute, 

 a* well as the relative altitude*, would have come out 

 very near the truth. We have already seen, howrter, 

 that the standard temperatures, as found by Mr. Les- 

 lie'* formula, are far too vague and uncertain to be em- 

 ployed in a calculation, where a single degree above or 

 Ix-low the truth produces an error of such magnitude 

 in the result ; and until these be verified by a more ex- 

 induction of farts, the :ilx>ve coincidence must 

 be regarded u* purely accidental. 



In April 1813. we instituted a serif, of observation* Riperi- 

 on the temperature of water raived by an excellent menu to 

 i, from the depth of 25 feet, and continued them -"certain 

 till September IHKJ. The result* of the whole shew 'h*'""- 



that, even at this depth, the fluctuations of temperature P* turt 



i i i ii i ' l " c | n- 



are very considerable; but we sh -II confine ourselves ler | or O f 



to the observations of the two entire years, 1814 ami ii,.- ground, 

 18)5, that we may have .in opportunity of comparing by means 

 them with the means of the daily extremes in tlie open "' I'ump 

 air. For a few months of 18 It, the maximum and mi- w " r - 

 nimum were not observed, but the blank has been fill- 

 cil ii|> Irom other observations, which have been found, 

 for a series of year*, to bear a certain relation to the 



