92 GAUSS AND WEBER ON TERRESTRIAL MAGNETISM. 



ner, what has been stated at p, 50. In the register of the 

 Marburg observations, which on that occasion were made in 

 the absence of Prof. Gerhng, and at the hours of 12''0">, 12>'5'n, 

 and 12^ 10"^, there appeared an unusual irregularity, which ex- 

 cited the suspicion, that about 12i* 5"" a spider had prevented the 

 free motion of the needle by attaching a thread ; and this sus- 

 picion was increased by the circumstance, that from 12ii 10™ to 

 the end the changes of the needle were exactly similar to those 

 which resulted from obsen'ations at other stations, but appeared 

 proportionally much smaller than could have been expected from 

 the experience of other terms. Prof. GerUng was requested, on 

 his return to Marburg, to examine the apparatus carefully, and 

 the resvilt is contained in a letter from the Professor. 



The examination took place on the 5th of November, up to 

 which time no one had entered the room of obser\'ation since 

 the September term. In the first place the position of the 

 needle was determined and found as follows : 

 at 3^ 33«» . . . 445-63 

 35 . . . 445-73 

 37 . . . 445-71 

 Upon this the needle was set in moderate vibration by means 

 of the moderating bar, and hence a time of vibration of 1 7 seconds 

 was fovmd, being nine seconds less than the usual duration : the 

 lid of the casewas then carefully removed, and avery minute li\ing 

 spider was noticed on its under surface ; a very small, and nearly 

 imperceptible, thread was thought to be observed hanging to it : 

 further, a number of small, black point- like bodies were found 

 in the box, which, under the microscope, proved to be the dead 

 bodies of gnats ; and finally, in one corner of the box, a regular 

 undisturbed web, of such fine texture, that without the reflexion 

 of the light it woidd hardly have been perceptible. From all 

 these circumstances it may be supposed that the spider had 

 been some time in the box. 



When the finger had been passed round the magnet bar in 

 aU directions, new observations of the time of vibration gave 

 again the former value of 26 seconds. The position was also 

 found to correspond to much lower numbers on the scale, 



namely, 



4^ 43°* . . . 431-45 



45 . . . 431-46 



47 . . . 431-12 



