\66 PHILOSOPHICAL TRANSACTIONS., [aNNO 1751. 



em lights rose to the zenith or passed southward, so as that the declination 

 seemed to follow the motion of the light, and in a very few minutes of time 

 would sometimes vary 3 or 4 degrees. M. Wargentin has also, by observations 

 in Feb. 1730, like as Graham, Celsius, and others, observed before, found 

 that there is a diurnal variation of the needle backward and forward : so as that 

 from 7 in the morning till 2 afternoon, the needle declined more and more to 

 the west by -f or -}- part of a degree ; after which it gradually returned again, so 

 as by 8 at night to be nearly the same as it was at 8 in the morning. After this 

 it is nearly at rest during the rest of the night, except some small motion to 

 the west about midnight. And this diurnal variation never fails, but is constant 

 and almost regular, unless when it is impeded by the northern lights. This he 

 observed constantly from the 1st of February to the 15 th, on which last day an 

 aurora borealis appeared, and deranged the needle so, as in 10 minutes time, 

 about 10 at night, it shifted 20' to the west, and in another ten minutes 

 returned thirty-seven minutes to the east. But on the lights disappearing, 

 the needle settled at rest. And thus it continued in its regular diurnal vibrations, 

 till Feb. 28, when it was again disturbed by another appearance of the northern 

 lights, so as to cause the needle to vibrate irregularly between 6° 50' and 9° l' of 

 west variation. And on the 2d of April, from a like cause, it differed from itself 

 little less than 5°, shifting irregularly and frequently backward and forward, be- 

 tween 4° 56' and Q° 55'. 



Xf^IlL Abstract of a Letter, dated May 2, 1750, from Mr. Freeman at Naples, 

 relating to the Ruins of Herculaneum.* p. 131. 



About 7 or 8 years ago, the discovery of Herculaneum was much spoken of, 

 which was reported to have been swallowed up by a violent eruption of Mount 

 Vesuvius, according to the last accounts, in the first year of the reign of Titus, 

 79 years after Christ. The situation of this city is at the foot of Vesuvius near 

 the sea, and just at one end of the village of Portici, the summer residence of 

 the king of Naples ; and probably a great part of the city is under the said 

 village. 



You are first conducted down a narrow passage, scarcely wide enough for 2 

 persons to pass ; and in a gradual slope, to the depth of about 65 feet perpen- 

 dicular. Here is shown a great part of the ancient theatre, a building in the 

 form of a horse-shoe. That part where the spectators sat, is visible, and consists 

 of 18 rows of broad stone seats, one above another, in a semicircular form. At 

 proper distances within the circuit of the seats, through the whole range, from 

 bottom to top, are little narrow flights of steps, by which the spectators might 

 come to, or go from, their seats commodiously, without crouding. These steps 



* See some former accounU of these ruins, vol. viii, p. 435 — 138, vol. ix, p 36'.' of these Abridg- 

 ments. 



