Mathematics.- Dodgson (Charles Lutwidge), "Lewis Carroll". Formulæ. (Group C.), with Dodgson's manuscript corrections in purple ink, bifolium, 220 x 142mm., a little light spotting, Oxford, 1878.

⁂ A very good copy of this rare cyclostyled pamphlet with manuscript corrections by the author in his characteristic purple ink. Dodgson said of his 'electric pen', which he acquired in 1877 that it 'seems to be quite the best thing yet invented for taking a number of copies of MSS, drawings or maps. The "pen" consists of a needle, in a holder like a pencil: the needle is worked in and out with enormous rapidity by electricity and projects far enough to go through a thin sheet of paper... the paper thus prepared is placed in a frame with blank paper underneath, and an ink roller is passed [over it]... copies are easily worked off at a rate of 2 a minute'.