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. Gerling, and at the hours of 12h0m, 12h 5m, and 12h 10m, there appeared an unusual irregularity, which excited the suspicion, that about 12h 5m a spider had prevented the free motion of the needle by attaching a thread; and this suspicion was increased by the circumstance, that from 12h 10m to the end the changes of the needle were exactly similar to those which resulted from observations at other stations, but appeared proportionally much smaller than could have been expected from the experience of other terms. Prof. Gerling was requested, on his return to Marburg, to examine the apparatus carefully, and the result 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 observation since the September term. In the first place the position of the needle was determined and found as follows:
| at 3h | 33 m | . . . | 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 17 seconds was found, being nine seconds less than the usual duration: the lid of the case was then carefully removed, and a very minute living 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 all 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,
| 4h | 43m | . . . | 431·45 |
| 45 | . . . | 431·46 | |
| 47 | . . . | 431·12 |
