go PHILOSOPHICAL TRANSACTIONS. [aNNO 1725. 



Exper. 6. The needle being turned, and standing as in the 2d and 4th ex- 

 periments, 



It performed the first 25 vibrations in 2"" 00*; the next 25 in 1™ 57*^; the 50 

 vibrations in 3"" 57^; that is, each vibration in 4\74. The dip being 74" lO'. 



Exper. 7- He now touched the needle at both ends with the same stone, 

 with which it was touched in the 5th experiment, after which 



It performed the first 25 vibrations in l"" 35' ; the next 25 in 1™ 34'; the' 

 50 in 3"' 9'; that is, each vibration in 3\78. The dip was 7'f 20'. The dip 

 repeated with the needle taken off and replaced 74° 20'+ • 



Exper. 8. On shifting the needle, it performed 



The first 25 vibrations in 1"' 33'; the next 25 in l"" 34'; the 50 in 3'" 7'. 

 The dip being 74° 25'. The dip repeated 74° 30'— . 



N. B. The needle had the same side to the east in the 1st, 3d, 5th, and 7th 

 experiments; and had that side turned westward in the 2d, 4th, 6th, and 8th; 

 and Mr. G. began to count the vibrations, when he observed it to vibrate just 

 10°. All these experiments were made with sufficient care in every particular, 

 excepting the quantity of the dip, which requires the divisions of the semicircle 

 to be very equal, and the 90° to be perpendicularly under the axis of the 

 needle; this last he found was a little faulty, the dip being in reality greater 

 than the semicircle showed it. After rectifying this error, and now touching 

 the needle, upon that part of the armour to which iron is applied, when it is 

 to be lifted by the stone, it performed the same number of vibrations in less 

 time than in any of the former trials. He now determined to observe, for some 

 space of time, both the dip and vibrations, without fresh touching the needle. 



The observations follow, by which it appears there is a very considerable differ- 

 ence, both in the quantity of the dip, and in the quickness of the vibrations. 



In all these experiments, the needle was placed, so as to vibrate exactly in 

 the plane of the magnetic meridian ; and sufficiently distant from all iron that 

 could afTect it, as far as could be perceived, till he had occasion to put up a 

 very large iron rod in the room above it, which immediately altered the dip of 

 the needle, and thereby put an end to these trials. 



The experiments are then recorded, as made at several hours of every day, 

 from March 29 to May 2, 1723; the quantities of dip differing from each 

 by only a very few minutes of a degree. The greatest was 75°, and the least 

 74° 20' : the medium of all, nearly 74° 40'. 



The vibrations of the needle, also observed at the same times, were, the 

 100 vibrations in all intermediate intervals of time, between 6"* 12' the greatest, 

 and 4*" 58' the least; the medium of all being nearly 5"" 35', the time of per- 

 forming 100 vibrations. 



