76 LECTURE X. 



The inks of the ancients are said to have been made of a carbonaceous 

 substance, and the modern Indian ink owes its blackness to similar materials. 

 Common writing ink consists of a gallate of iron, suspended by means of 

 a little gum ; the sulfuric acid, which remains mixed with it, is probably 

 of no consequence to its blackness. It has been observed, that an abun- 

 dance of the gallic acid produces a much blacker colour than is obtained 

 where this acid is used in a smaller proportion. Mr. Ribaucourt's method 

 of making ink,* is to boil eight ounces of galls, and four of logwood, in 

 twelve pounds of water, until the quantity is reduced to one half ; and, hav- 

 ing strained the decoction, to add to it four ounces of sulfate of iron, one of 

 sulfate of copper, three of gum arabic, and one of sugar candy. But for 

 ordinary purposes, it is sufficient to infuse three ounces of galls for a day or 

 two in a pint of water, and to add to it an ounce of gum arabic, half an 

 ounce of green sulfate of iron, or copperas, and a drachm of sulfate of cop- 

 per, or blue vitriol, or even a much smaller quantity of gum and of copperas, 

 if a very fluid ink is required. The sulfate of copper produces a durable 

 stain, but it does not immediately add to the blackness of the ink : its 

 principal use is to counteract the tendency of the ink to become mouldy. 

 Sometimes a mercurial salt is employed for the same purpose, and a little 

 cotton, if the inkstand is too open, is also useful in preserving the ink ; 

 but the addition of spirits is often insufficient, and is liable to make the 

 ink run. 



It has been proposed to use inks of different colours for indicating 

 different numbers ; so that by ten kinds of ink applied in different ways, 

 any numbers at pleasure might be expressed. Thus, in making an index 

 of the words of an author, each page might be readily covered with lines 

 of different colours drawn in different directions, so that each word, when 

 cut out, might indicate the page to which it belongs. 



An ingenious instrument has lately been constructed, by means of 

 which copies may be multiplied with great facility ; it is called the poly- 

 graph, and consists of two or more pens, so connected by frames and 

 springs, as to move always in parallel directions, each having an inkstand 

 and a sheet of paper for itself.t In this manner five copies may be made 

 at once with tolerable facility, and the method may perhaps hereafter be 

 extended to a much greater number. 



A mode of writing, perfectly different from any of those which have 

 been mentioned, is performed by means of the telegraph, which is justly 

 considered as the invention of the ingenious Dr. Hooke.:}; The ancients 

 had attempted something similar, by the exhibition of torches on elevated 

 situations ; but Dr. Hooke observes, that the addition of the telescope is 

 absolutely necessary for the practical success of the process; and the 

 directions which he gives for its performance differ very little from the 

 plan which has since been generally adopted, first in France, and after- 

 wards, with some variations, in this country. Dr. Hooke proposed the 



* Repertory of Arts, ix. 125. 



f Cotteneuve, Mem. de 1'Acad. Paris, 1763, H. 147. 



J Ph. Tr. 1684. Philosoph. Exp. and Obs. bv Hooke, edited by Derham, 

 p. 142. 



