BY J. C. BRUNNICH, F.1.C. 43 
used in his calculations and he can fix them by making 
marks either on the rule or on the slide. Movable metal 
runners, called cursors, which have a fine vertical line marked 
on a piece of glass, facilitate in many cases the »perations 
and the setting and reading off, but are particularly useful 
in continuea operations like a.b.c.d.~e.f.g. 
I may here add that for office use slides with the scales 
arranged on circles have been constructed, which, however, 
have no advantage over the slides already mentioned. 
Another pocket arrangement is a scale invented by Proell, 
on which we have a scale divided into ten equal parts printed 
on a small card, and a similar scale printed on a transparent 
sheet of celluloid, which is moved on top of the scale on the 
cardboard. 
I trust that the examples I have given are sufficient 
to clearly demonstrate the value of mechanical and graphical 
aids to calculations, and so that they may be more commonly 
be used as time and labour saving inssruments. 
In order to enable any student to get some more in- 
formation on this interesting subject, J will enumerate a 
few of the publications dealing with graphic calculations 
and slide rules :— 
L. Lalanne.—Memoires sur les tables graphiques et 
sur la géométrie anamorphique. 
do. Méthodes graphique pour l’expression des 
lois & trois variables. 
Lallemand.—Les abaques hexagonaux. Feuilles litho- 
graphiées en 1885. 
M. d’Ocagne.—Nomographie.— Paris, Gauthier Villars. 
do. Sur une méthode nomographique. ‘‘ Comptes 
rendues de l’académie des science,” juillet 1893. 
L. Lalanne.—Instruction sur les régles a calculs. 
—Paris. 
Quintino Sella.—Teorica and pratica del regola cal- 
colatore. Torino. 
Elhot.—A treatise on the slide rule. London. 
A. Beghin.—Régle a calculs. Paris. 
C. N. Pickworth.—The Slide Rule.—Emmott and Co. 
Manchester and London. 
MS) BR: Pressler. — Mathematisch — Polytechnische 
Brieftasche mit Ingenieur Mess-Knecht.—Wien. 
Moritz Perles. 
