( 20 ! ) 
uftirpatis, levatnen percepir. Laborat autem ifla 
obftrudtione raenfium, quas mali huhus fons at- 
que origo efle videtur. 
JVittenbergte D. i Auguji. 
A. D. Mdccxxxv. 
X. Experiments concerning the Vibrations of 
Pendulums. By the late W. Derham, 2). 2>. 
F. 2^. S. and Canon of Wind for. 
T H E Account which Mr. Bradley hath given 
in Fhilofoph. TranfaQ. N° 432, of Obferva- 
tions made at Jamaica by Mr. Campbell with a 
nice Fendulum-Clock of Mr, Graham's making, 
brought to my Mind fome Experiments I made 
fome Yearsago, that may be of Ufe in Obfervations 
of rhis nature. 
The firft that I fhall take notice of, fhall be fome 
Experiments 1 made in the Year 1704, with ex- 
cellent Inftruments, concerning the Vibrations of 
Tendulums in Vacuo ; which were publilhed in the 
Fhilofoph . TranfaEl. N° 294. The Sum of which 
is, That the Vibrations in Vacuo vcz re larger than 
in the open Air , or Receiver unexhaufted : Alfo 
that the Enlargement or Diminution of the Vibra- 
tions, was conftantiy in Proportion to the Quantity 
of Air, or Rarity, or Denfity thereof, which was 
left in the Receiver of the Air-Pump. And as the 
Vibrations were larger or Ihorter, fo the Times 
Were augmented, or diminilhed accordingly ; viz. 
two 
