166 V. WALFRID EKMAN. 



action of two spiral springs ^ raise tlie platform attached to the 

 narrow rods, r, r; the point of the pendulum pierces the cork 

 plate of the platform, and is thus fixed, as the before-mentioned 

 head, e, at the upper end of the pendulum, is now pressed lightly 

 against the screw above it. 



The magnetic needle, t, and its arresting mechanism are seen 

 in section; in fig. 2 arrested, and in fig. 3 free. As it proved to be 

 not very satisfactory in action, and ought not to be imitated, it 

 is hardly necessary to describe it. It consists of a plate with 

 teeth round the periphery as in Aimé's current-indicator, but 

 these teeth are apt to strike the compass-needle off its point, so 

 that the lid has to be removed, and the needle replaced. It might 

 be better to make the arresting plate in the form of a conical 

 ring, and the magnetic-needle with obliquely truncated ends, which 

 fit into, and rest in, the ring, when it is lifted from its pivot. 

 The movable arresting platform, which several times refused to 

 act, ought to be replaced by a stationary one, and instead the 

 pendulum should be forced down against the platform, a work 

 which the messenger might easily be made to perform. 



These are, however, unimportant, practical details. There 

 are also several other small improvements to be made, as is 

 very natural, this being the first experimental apparatus. In all 

 essential points, on the other hand, the instrument acted excee- 

 dingly well, showing that its principle is happily chosen. 



Before proceeding with the account of the observations, I will 

 relate, in connection with the description of the apparatus, the 

 experience gained concerning the manner in which the appa- 

 ratus should be used, and its trustworthiness, etc., in support 

 whereof the reader is referred to the following account of the 

 experiments. 



As already mentioned, the apparatus is principally intended 

 for observations from ice, and the greater number of these first 



1 Since replaced by india-rubber bands. 



