242 



Mr Galbraith on Kater'^s Azhnuth Circle. 



To shew you what my little circle will do, I send you eight 

 single observations of the pole-star made on different evenings, 

 (being the whole I have made here,) with three different instru- 

 ments constructed for my friends. These observations might 

 have all been made the same evening, and the difference of the 

 mean from the truth is only 4."83, my latitude being very 

 nearly 5V 31' 91" N.''— Captain Kater then resided at No. 2 

 York Gate, Regents Park, London. 



Observations referred to. 



" But the first observation should, by rights, be rejected, 

 having been made with an instrument scarcely finished, and 

 much out of adjustment. In that case, the mean of the re- 

 maining seven would be only — 1".69 from the truth. Such, 

 then, are the results of an observer of great experience, and 

 of undoubted veracity, and they shew in a remarkable manner 

 the great precision which may be obtained by instruments of 

 very moderate dimensions. In another letter previous to the 

 above he remarks, — 



" The circle you describe as of six inches diameter is too large 

 for my construction. The size I recommend, and which I use, 

 is only three inches diameter, and in the latest construction it 

 has only a vertical circle, which can, however, be placed in the 

 plane of two objects so as to take the angle between them. The 

 whole is contained in a box seven inches long. Jour and a half 

 wide, and three deep, so that it really deserves the name I ori- 

 ginally gave it, of a pocket azimuth and altitude instrument.*" 

 Such an instrument may therefore be, we think, strongly recom- 

 mended to the notice of scientific travellers with perfect confi- 

 dence. 



