and Levelling, fyc. 34o 



cause to attribute this I cannot positively say, though partial 

 local attraction is sufficient to account for it, since, in other 

 situations, it has been known to produce greater discrepancies 

 between the observed and geodetic latitudes than what has 

 been here determined. No doubt, in the course of time, future 

 observations will be made in greater number, and with supe- 

 rior instruments to mine, in order to explain this anomaly in 

 a satisfactory manner. I cannot, however, understand how, 

 on any other principles than those of local attraction, my circle 

 should give results agreeing with those of the mural circle at 

 one place, and disagreeing at another. Till then, I may be 

 allowed to infer from the observations I have made and de- 

 tailed in the preceding paper, that the anomaly is owing to a 

 partial local attraction at the Calton Hill, whereby the plumb- 

 line is deflected towards the south, thereby throwing the 

 zenith point towards the north, making the observed latitude 

 exceed the true by about G" or 7". 



1. In assuming the decrement of heat at 240 feet for 1° 

 Fahrenheit in this country in the preceding investigation, as 

 being sufficiently accurate for my present purpose, I still ad- 

 here to my conclusions in a former paper on that subject read 

 to this Society, namely, that the law of decrement involves 

 functions of the height and latitude, which is borne out by the 

 fact, that the decrement for considerable heights, and for 

 high latitudes, is greater than that derived from small heights 

 and low latitudes. It is, generally speaking, greater from 

 Ramond's great heights than from smaller, and that from 

 the barometric observations of Captains Sabine and Foster to 

 determine a height at Spitzbergen, in latitude 80° N., there 

 was no sensible change of temperature for an elevation of 

 1640 feet.* From these remarks it would also follow that 

 the decrement will also change with the season, and also with 

 the hour of the day. This is partly the reason why even the 

 astronomical refractions in the Arctic regions were found by 

 the late Captain Foster to be very different from those in 

 more temperate climates. 



* From" a mean of the whole. Some of them indeed indicate a greater 

 temperature at the top than the bottom. 



