38

the semidiameter of the Ball maketh the Length of the vibration from the point of suspen
=sion to be 15 inches, and the Line of the Ball of 6 inches Diameter was 12 inches Long wch
added to the semidiameter of this Ball maketh the whole Length to be 15 inches. In
the 2d tryall it was as before. except that the pendulum wth. the Ball of 3 inches was ad
Iusted to 13 11/20 inches to make it vibrate equally wth the other two. This being calculated
& compared wth. mor. Zulichems Rule was found to approach very neer to it.
mr. Hooke was orderd to attend the Prest. on Fryday next to adjust the Pendulum to vibrate Seconds
(sceptis scientifica) mr. Hooke gaue some Account of the Expts. of Refraction made by him
since the Last meeting. wth the solutions of vitrioll salt peter and Allum in Water where he had
found the Refraction of the Sol: of vitrioll & salt petre a Little more, but that of Allum
somewt Lesse then that of Salt petre common water. Orderd that the next Day
the whole tube of the Refracting Instrument be filled with the Liquor whose Refraction
is to be examined and the glasse be putt at the Lower end exactly set at right angles to
the tube as also that these expts. be made wth Seuerall quantitys of the Liquors, and
In vessells of Seuerall sises and that wth. Liquors turbid & Coloured as well as cleer -
(mr Henshaw frog spawn) Ld Breretons Bred ale) Catalogue of trade . BP. of Exeter had one printed)
(expts. of cold. 1 a standerd for it. 2 Loadstone in Ice. 3 Ice wthout blebbs. 4 freezing exhausted water
orderd that these expts. be made by mr Hooke when the weather serveth. The same orderd
to bring in the Scheme for the Instrument to measure the Refraction which Celestiall bodys
suffer in the air. Item to haue his quadrant made for Discouering a 2d minute by the starrs
Item to try next Day mor. Zulichems way of thermometers. wth a cane of salt water and a
ball of glasse swimming in it (paper about ordering vines)
Decemb: 14. 1664/5 (culture of vines) The Expt. of mor. Zulichem of making a thermometer
with a Cane of salt water and a glasse ball poised in it was tryd and It was found
that the glasse Ball did Rise & subside according to the alterations of heat & cold, orderd
that it be kept & compared wth the other Thermometers to see whether it be soe nice &
sensible as they (Austins proposalls about fruit & timber trees.) expt. of cutting 6th. pair of nerues
in Days) Dr. wrens optick Lecture in Gresham Colledge Desired.) account of Dr Henshaws booke)
The Expt. of monr. Zulichems for the vniuersall measure was Repeated this day twice, and
the first time the string of the Biggest Ball which was of 6 inches Diameter was
2 foot 11 4/5 inches Long and that of the smaller Ball was 3 foot 1 1/2 inch Long the
President hauing calculated the proportions accordingly to mor. Zulichems Rule
found them vary from it 1/10 the string of the smaller bullet being 1/10 longer then It
should be according to that Hypothesis. in the 2d tryall the Difference was yet
greater vizt. 1/10 & 1/20 or 3/20 which was thought too considerable a difference for a stan
=derd. It was herevpon concluded that there must be either some mistake in the Rule or
some fault in the expt.

q whether length doth not vary in differing countrys

the Pt. hintedthat the Difference of the air & the Bullet may vary the Length of the Length
of the Line soe that a small bullet in a cleer air & a great Bullet in a thick air
will cause Different measures
mr. Hooke suggested that It would be best to make Pendulums of the shortest Length
considering that a Little Variation in Length maketh a great alteration in time
The same produced a paper conteining certain considerations of his about the Vni
versall /(very blotted out)/ measure, It was orderd to be registred as conteining Ingenious suggestions
He gaue also some account what he had done at the Ld Brounkers house adjusting
the Pendulum to vibrate seconds . vizt that my Ld Br: Pendulum vibrating Iust seconds
went a Little quicker then those tryd at Gresham Colledge for seconds . and that the
Length of the Pendulum for seconds at my L. Br: was 3 foot 1 2/5 and the Ball of
3 inches Diameter. The Expt. of trying the Refraction of common water by filling
the whole tube of the Refracting Instrument wth it was tryed and It was found
that it agreed wth the vsuall way of trying the Refraction of that Liquor.
mr Hooke produced the scheme for the Instrument of measuring the Refraction
[In margin]Vz.   of Celestiall Bodys in the air It was orderd to be Entred:
Decemb: 21. 1664 (comet accounts) mr. Palmers seal metall made by a gentle wooman
which could harden & reduce it to a Lesser form.) welsh Pearles. core black in the middle .

Ref: CELL/RS/HF_040  © Centre for Editing Lives and Letters