2 
3 
1810.] Graduation of Philosophical Instruments. 331 
of reading off minute divisions on the the purpose of subdividing other divisions 
tables of philusophical instruments, ame- by means of a moveable scale; hence it 
thod presented itself to me, by. which might commence where divisions in the 
apparently the present way of graduating present way are found to become irk- 
instruments might be much iunproved. 
The method I mean, and which, as far 
as I know, is perfectly new, is, instead 
of engraved or black lines with spaces 
between them, to use lines of the di- 
mensions required, of different colours, 
in contact with each other: thus the 
some to reckon, viz. at the bundred in 
the inch, dividing in this instance any 
tenth of an inch into ten, thus giving 
hundredths; any hundredth of an inch 
into ten, giving thousandths; and so on 
to any required or possible extent.* 
Ti will be apparent, that having pres 
spaces, which in the present way occupy , viously assigned a specific number to 
room, without forming a part of the cal- 
culation, would be entirely done away, 
and every set of divisions upon an equal 
scale would be comprized in at least half 
the compass. 
The divisions in present use, are to the 
tenth, twentieth, or fiftieth of an inch: 
A greater minuteness than this quickly 
becomes irksome in practice. 
The. divisions above-mentioned, are 
afterwards subdivided by means of a 
vernier, so as to extend to the hundredth, 
thousandth, and even ten-thousandth of 
an inch, by means of a good magnifier ; 
and here the difficulty I have alluded to, 
of caleelation, is increased. 
My method is, to use ten lines, each of 
a different colour, contrasted in the best 
manner, each being as strongly tinted as 
possible, and placed in contact with each 
other. The order of the colours I have 
adopted, is represented in the following 
sketch: 
Beye Le sees ee | Goy Cp Ss} 
Sore SS (Ve Sas I Pe es Ti Fe ee 
| Feel ey petra Cais (coli thas) hand [ero (hee 
Stato pe LO takes | = let = 
sabes Teh aie | S15) 24° 
> . 
Fe ennnamnemmned 
10. 9, 3. cs 0. ie 4. Die Be 1 
the whole running in the order here ex- 
hibited ; and assigning the number spe- 
cified, respectively to each of the several 
colours, so that each colour shall signify 
or express that number. 
Having found some difficulty in pro- 
enring such lines of colour, drawn with 
the required exactness, I succeeded com- 
pletely to my wish, by placing together 
laming of card, paper, or tm-fcil, com- 
pressed together, as it were, into one sub-_ 
stance, the edge of each lamina having 
been previously prepared with the pro- 
per colour. 
By this method, experience has proved 
to me that divisions to the number of a 
hondred in an inch can be easily read off 
by an ordinary eye, unassisted by a mag- 
hifier; and to two thousand by a mag- 
nifier of ordinary power. 
It will be obvious that this method by 
coloured Jines, is applicable chiefly to 
4 3 
every different colour, which after a little 
practice would berccollected, but which 
might at all times be instantly known by 
referring to a similar scheme upon a 
scale of convenient size ready for the 
purpose, the trouble or irksomeness of 
reckoning minate divisions would be en- 
tirely obviated; the line of colour pointed 
at, indicating at once the number of sub- 
division, 
In descending to extremely minute di- 
visions, the moveable scale, instead of 
containing ten lines of colour, might have 
one-half only, in coloured lines; which 
would be sufficient fur imdicating any 
number of the ten, the blank space of 
the scale indicating fivé occasionallyt. 
This ntode of division admits in course 
the use of the vernier, consisting in 
this instance of coloured lines, as well 
as in the usual method, and with at least 
equal advantage. : 
A scale of division consisting of 10,000 
in the inch, is sometimes required in 
practice; and doubtless minuter divi- 
sions still might be desirable, were they 
made so as to besee. ind reckoned with 
facility; which, I flatter myself, the me- 
thod here proposed will be found per- 
fectly adequate to, : 
n my experiments I made use of card, 
paper, and un-foil, as I have mentioned 
above, merely by way of trial; and having 
found thein answer, I should recommend 
the use of Jamire of brass, copper, or 
silver, which, compacted together into 
seer | Sy eee gets YS 
* I am informed from unquestionable au=- 
thority, that microscopes are made for sale 
which magnify tke diameter of an object 600 
times: hence it will foilow that such di- 
‘visions as | have mentioned, might be ex. 
tended tothe number of 60,000 in-the léngth 
of an inch, provided coloured laminz suffi. 
ciently thin could be procured, or an artist 
had dexterity enough to draw such coloured 
‘dines. 
+ Whenever five colours only are used, 
perhaps the following arrangement might be’ 
the.best: 1 white; 2 blue; 3 red; 4 yel- 
low; 5 black. | re 
one. 
