304 PHILOSOPHICAL TRANSACTIONS. [ANNO 1772. 



ing on the arch, and thence also find the instrumental angular distance of the 

 object and mark. Take the sum of this and the former instrumental angular 

 distance ; half of its difference from 36o° will be the correction, which added to 

 the instrumental angular distance first found, between the same direct object and 

 the other object seen by reflection, will give the true angular distance between 

 them, reduced to the centre of the index glass. 



It is to be observed, that if the mark be set up at the same distance from the 

 quadrant as the direct object is, there will be no occasion to invert the plane of 

 the quadrant, but the observer need only make the image of the mark coincide 

 with the direct object, then turn himself half round, and now taking the mark 

 for the direct object, cause the image of the former direct object to coincide with 

 the mark, the divided arch of the quadrant being kept upwards, and the place of 

 the centre of the quadrant remaining also the same in both cases : half the dif- 

 ference of the sum of the two instrumental angles from 36o degrees, will be the 

 correction of the adjustment as before. Should only one of the objects be near, 

 and the other remote, viz. half a mile distant or more, let the distant object be 

 taken for the direct one, and the near object for the reflected one ; then the true 

 distance of the objects, as seen from the centre of the index glass, will be ob- 

 tained without requiring any correction, whether it be the back or fore obser- 

 vation that is made use of; only observing, as usual, to take the supplement, of 

 what is shown on the arch, to 180 degrees, in the back observation. 



Xy^. Account of the Jrmplion of Sdivay Moss, on Dec. l6, 1772. By Mr. J. 



Walker, of Moffat, p. 123. 



It is not surprizing that this irruption has every where attracted the atten- 

 tion of the public; for though the cause of it is obvious, yet the alteration that 

 it has produced on the face of the earth seems to be greater than any we have 

 known in Britain, from natural causes, since the destruction of Earl Goodwin's 

 estate. It happened on the l6th of December, when there fell such a deluge of 

 rain, over all the north of England, as has not been known, for at least 200 

 years. There was a very great flood at Moffat, but Mr. W. thinks he has seen 

 one or two greater, and certainly it was not so extraordinary here, as far- 

 ther south. 



The Solway flow contains 1 300 acres of very deep and tender moss, which 

 before this accident were impassable, even in summer, to a foot passenger. It 

 was mostly of the quag kind, which is a sort of moss covered at top with a turf 

 of heath and coarse aquatic grasses; but so soft and watery below, that if a pole 

 ''is once thrust through the turf, it can easily be pushed, though perhaps 15 or 20 

 feet long, to the bottom. If a person ventures on one of these quags, it bends 

 in waves under his feet ; and if the surface breaks, he is in danger of sinking to 



