( ) 
The laft thing I fliall deduce fhail be by way of Querey r?/>. 
Whether the Variations of Pendulums obferved under the Equl- 
noflial, and between the Tropicks^ -do not arife as much or more 
from, the rarity of the Medium^ and the encreafe of the Vibntions 
confequent thereupon ? It is fcarce I think to be doubted, but that 
the Air is much thinner, and finer near t^e Line, than ic is with- 
out the Tropicks. And it is evident from the Barometer^ that on 
the tops of high Mountains the Atmofphere gravitateth lefs than 
nearer the Center. And therefore (although I like he Notion of 
the Decreafe of Gravity from the Encreafe of the diftince from 
the Earth's Center ^ I fay, although I like this too well to difcard 
it, yet) I am apt to think that this is not the only reafon of the- 
'2hc€nomenon\ 
I vYifh therefore that Captain Ualley^ when he obferv%l at St 
Helena his Clocks to go flower than in England^ had at the fame 
obferved whether the- Vibrations were not enlarged. It might be 
tlieretore very well worth the while for fuch as have opportunity, 
to rake notice. Whether their Pendulums becween the Tropicks 
do not make larger Arches than in higher Latitudes > Alfo in what 
Latitude they begin to alter > Whether the Vibration be greater 
near the Line, than in any other part between the Tropicks Or 
whether the greateft encreafe be not always in thofe places where 
the Sun paffeth their Zenith ? If the Vibrations be found larger 
under the Line, or in any other part of the Torrid Zone, then it 
may be obferved, how much larger they aie^ and in what propor- 
tion they encreale, or decreafe, by approaching nearer unto, or 
receding from the place of their greateft Encreafe ? 
Alfo it may be worth obferving, Whether Pendulums do not 
vary on the tops of high places, .or in difterenr ft ices of the At- 
mofphere, accl)rding as the Mercury is high or low in the Baro- 
meter } But then in this, and indeed .in the former c fes, it|is necef- 
fary, or atleaft very expedient, .that the Move:nent be fo exa£tly 
well made, that the Power, whether Weight or Spring, do at all 
times exert the very fame force upon the Pads or Pallets. Which 
is very rarely met with. For molt Clocks are ape to vibrate fome- 
times larger, fometimes lefTeA Arc :ies in the 24 hours, according 
as the Weight or Sprmg doth vmiQ 01 lefs exert lis far^^es on the 
work. " 
Thus having given the Society the account vtdiich they com* 
mandedme if I have nor anfwered thci? Ey.pe£l:a!:lcn, yet I have 
however ftiewed my Obedience to theii Commaiids and given a . 
Teftimony ofmy great Veaeiudon tor chit Inge uoas and Learnect 
Body. ^ 
