HOROLOGY. 
364 
interval neceffary to maintain its movement when it re¬ 
ceives an impulfe from the balance-wheel. A fcapement 
on the plan hinted to Mr. Matthew, would be both a free 
fcapement, and have the advantage of Mudge’s contri¬ 
vance for cutting oft’ all irregularities of the train. Such 
a fcapement has been attempted by feveral, among whom 
may be mentioned Mr. Haley and Mr. De la Fons; but 
none of this kind as yet have been fufticiently free from 
complication to entitle them in this refpeft to any fuperi- 
ority over Mudge’s plan.” 
At the end of the fpecification, Mr. Matthew mentions, 
as a farther improvement to chronometers, the ufe of pla- 
tina for flopping the holes and other purpofes inftead of 
ufing hard brals and jewelling. This idea is certainly 
good ; indeed it would be a great improvement to fubfti- 
tute platina for brafs in the whole of the internal work of 
time-pieces, as it would prevent the injurious effects from 
the oil growing thick by chemical aflion on the metal. 
The price of it could be no ferious objection, and it can 
be forged almoft as eafily as fteel; balances for watches 
have already been made of it, and feveral artifts now’ know 
how to-manage it very w'ell. 
Barraud's Time-keeper. —We muft not omit to mention 
a longitude time-keeper made by an ingenious artift now 
living, Mr. Paul Philip Barraud, of Cornhill, which for 
accuracy of performance feems to be inferior to none of 
thole we have mentioned. It was taken to the Eaft Indies 
’by lord Keith in 1795, with fome of Mudge’s time-keepers 
and others. It is thus handfomely fpoken of by Mr. 
Mudge, jun. “A time-keeper made by Mr. Barraud was 
begun to be tried on the 7th of June’1795, and continued 
to be obferved till the 28th of Auguft following. The 
performance of this machine appears to have been, during 
that time, very excellent, the extreme difference of its 
daily rate with refpeft to No. 2, (Mr. M.’s time-keeper,) 
in the 72 days, being only 6"; and, where the conformity 
is fo great, the intelligent reader will be aware, that the 
errors are as likely to have been in the ffandard as in the 
time-keeper tried by it.” 
We might have added to our article an account of dif¬ 
ferent chronometers by French makers; but, as a chro¬ 
nometer differs from an ordinary watch principally in the 
cornpenfation-balance and fcapement, their properties and pe¬ 
culiarities of conftru£tion defcribed under thefe two heads 
will be amply fuflicient, after what we have here faid on 
the fubjeft. 
DireSions for the Ufe of Longitude Time-keepers. —The two 
moft effential requisites in ufing a time-keeper, are, firft 
to be able to afcertain its mean daily rate of going, and to 
apply it to the time indicated at any place and inftant 
.afterwards'; and, lecondly, to be able to determine by ob- 
fervations on fome of the heavenly bodies the exa£l hour, 
minute, and fecond, at the faid place and inftant of obfer- 
vation, becaufe the difference between the correfled time 
indicated by the watch, as the time at the firft meridian, 
and the equated time obtained by calculation from the 
obfervations, will be the exaft difference of longitude, in 
time, between the place of obfervation and the firft meri¬ 
dian to the time of which the chronometer is fuppofed to 
have been previoufly put. 
Though the rate of a time-keeper, as afcertained from 
a fucceflion of tranfits of a heavenly body be moft to be 
depended upon, yet it will not always happen, particularly 
in a changeable climate, that a fuflicient number of obfer- 
vations can be obtained within the limited time allowed 
for fixing a rate; it will, therefore, be very convenient to 
compare tfie going of the time-keeper with that of either 
a folar orfidereal clock, that has a compenlation-pendulum 
and good fcapement, and to afcertain in the mean time 
the rate of the clock itlelf by occafional obfervations of 
the fun or ftar, it being generally allowed that a good clock 
is more jleady in its rate than any chronometer which has yet 
been made, provided its adjustments be perfeft. It may 
be advifeable to try the time-keeper, in the rlrll place, in 
different pofitions, by fhort comparifons of 12 hours each 
with the clock; and, if any confiderable change of rate 
takes place during fuch fhort comparifons, it muft necef- 
farily be put into gimbols, or otherwife be fent back again 
to the maker for new adjuftment for the different pofitions. 
For a Solar Clock. —Place the chronometer in the pofition 
it is likely to prelerve in a voyage, and put its hands with 
thofe of the clock, and have a lheet of paper ruled into as 
many columns as the companion will require ; for a folar 
clock feven columns will anfwer the purpofe, but for a 
fidereal clock there will be more required. Put titles to 
the different columns, and, after an interval of each 24. 
hours, make the requifite comparifons, and enter them as 
they Hand in the lubjoined example, referving columns 
four and five to be filled up afterwards ; then, after as many 
days’ comparifon as the time will allow, complete the cal¬ 
culations in thefe two referved columns thus ; take a mean 
of the obferved differences between the time of the clock 
and mean time determined occafionally by a tranlit-inftru- 
ment, which will be the clock’s mean daily rate, parti¬ 
cularly if the obfervations are taken after equal intervals ; 
then add or fubtrafl, as the cafe may be, the clock’s daily 
rate to or from the refpeftive numbers in column three, 
and fill up column four with the fum or differences, or 
both, if the cafe fhould fo be; in the next place, take the 
differences between each couple of the lucceeding lines of 
column four, and fill up therewith column five, annexing 
— or +, as the difference may be ; laftly, take the dif¬ 
ference between the plus and minus amounts, or the fum 
if there is but one kind, and divide it by the number of 
days elapfed on trial, and the quotient will be the daily 
error, — or +, which error is denominated the rate. 
Example. Let it be required to aflign a rate to a chro¬ 
nometer from the comparifons made in the columns 1, 2, 
and 3, of the annexed table. 
Days of 
Trial. 
Clock af¬ 
ter mean 
Time. 
Chronom 
diff. from 
Clock 
in 24 h. 
Do. from 1 
mean 
Time in 
24 h. 
Dai 1 y 
Bate of 
Chron. 
Mean 
St te of 
hermo- 
meter. 
Mean 
State of 
Barome¬ 
ter. 
s 
s 
s 
O 
I 
— 6’S 
+ 
8-5 
+ 2’2 
54 
29’8 
2 
4 “ 
8-8 
4 - 2 '5 
4 - °'3 
55 
30*0 
3 
+ 
9'4 
4 3 'I 
—0 6 
57 
3 D *2 
4 
+ 
7’5 
4 - 1-1 
— i ’9 
56 
3°'4 
5 
+ 
9 '° 
4 - 2 ’7 
4 i '5 
53 
29-6 
6 
+ 
10*4 
4 - 4 'i 
4 - 1 ‘4 
53 
29-4 
7 
+ 
I O '5 
+ 4-2 
-j- O’l 
54 
29-6 
8 
— 8*o 
4 
ii’3 
4 - 5 '° 
-j- o’8 
55 
297 
9 
+ 
1 1’5 
4 - s' 2 
4- 0-2 
54 
29’8 
IO 
4 * 
10*4 
4 - 4 'I 
— I’l 
56 
30’° 
I I 
4 - 
IO'O 
4 - 3'7 
— 0’4 
57 
3°'4 
12 
4 - 
8-4 
4 2’I 
— i*6 
58 
3°'4 
13 
4 - 
7-6 
+ !'3 
— o-8 
57 
30-6 
14 
4 
7‘4 
4- i’i 
- 0*2 
5 6 
3°'5 
15 
— 4 ’S 
4 
7-2 
4-0-9 
- 0*2 
57 
3°'4 
3|ig° —6 - 2 Total lofs. 
Rate of? ” $ ++-9 Total gains. 
clock! -6 3 - 
on an average of % 13 * n 13 ^ a y s - 
15 days. J 
— i s- 3 
Then *- = 0 5, o87 minus is the daily rate of the 
chronometer taken from a comparifon with the clock for 
1 5 fucceflive days, which rate muft be added to the time 
ftiown by the chronometer on any fucceeding day, after 
it has been multiplied by the number of days elapfed fince 
the laft day of the comparifon. This rate might fuffice fora 
fttort voyage, immediately undertaken, if the chronometer 
had been tried and approved previoufly ; but, if not previ- 
oufly approved on a voyage, it ought to have a longer trial. 
For a Sidereal Clock. —When the clock ihows fidereal time, 
and the chronometer folar, their difference in 24“ of folar 
time 
