BUILD AN OBSERVATORY. 199 



difference of temperature between the out and 

 inside was 14°. There was not a nail or the 

 smallest particle of iron in the building ; and to 

 guard against the accidental approach of any 

 person with a gun, an axe, or the like, I had 

 it enclosed with a ring fence of seventy feet 

 diameter. It was situated on a gentle rise, two 

 hundred yards from the lake, and about one 

 hundred from the east end of the house. A 

 strong staff, fifteen feet high, was fixed on the 

 northern extremity of the ridge pole, on the 

 spindle of which was a vane ; and besides white 

 poles, placed in the direction of the true and 

 magnetic meridian, I had a horizontal cross at the 

 north side of the observatory, within the fence, to 

 enable us to take the bearings of phenomena with 

 greater accuracy than can be attained by the mere 

 guess of the eye. The angular heights of the sur- 

 rounding mountains were also ascertained. 



Observations were immediately made for the 

 magnetic force and dip, with Hansteen's and Dol- 

 lond's needles, and a lozenge-shaped one after the 

 suggestion of Captain Beechey ; but this, for the 

 sake of clearness, will, together with our observa- 

 tions of other phenomena, be thrown into a tabu- 

 lar form in the appendix. Three thermometers 

 (spirit) were placed inside the observatory — four 

 outside, on the north, and one exposed to the sun 

 on the south side. They had been previously 



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