B. DECLINATION. 



The determination of the magnetic declination was made by the aid of 

 two declination needles belonging to the apparatus, and furnished with mirrors, 

 in a manner similar to that with an ordinary NEUMAYER-Declinatorium. After 

 the instrument had been duly levelled, the telescope was pointed first at a 

 mark, with subsequent reading of both verniers of the horizontal circle; and 

 then a coincidence was effected, during the constant employment of the ivory 

 disc, between the wire of the telescope and its reflected image in the mirror 

 of the declination needle. From October 20th, 1893, to February 22nd, 1894, 

 and on subsequent rare occasions, the telescope could not be used on account 

 of fog, hoar-frost or unfavorable conditions of light. The setting was then 

 done with the naked eye, a vertical line introduced in the middle of the 

 glass of the magnet box, being employe das wire. The pin on which the de- 

 clination needle rested, was renewed several times, as there was a reserve 

 supply of pins, and also a special apparatus sent with the instrument, for 

 grinding and polishing the point of the pin, if any injury should befall it. 



THE NEEDLES. 

 THE DOUBLE DECLINATION NEEDLE. 



The needle intended for the declination observations proper, was a double 

 one, that is to say, it consisted of two laminae, between which the mirror was 

 fixed. Its weight was only 29.05 grammes, and as it was made to reverse, 

 there was always an opportunity of determining, or eventually eliminating, 



