PALPABLE MATHEMATICS. 191 



but it has the inconvenience of preventing perfons that can fee 

 from reading it, unlefs they have alfo praciifed the fame me- 

 thod *. 



A black writing may Iikewife be obtained with this iron pen, How to make 

 by placing on the writing paper another flieet done over with ^ e wmin g «$»- 

 hogs-lard and ivory black, covered again by another, through 

 which the letters are traced. The inconvenience of this me- 

 thod is, that the blind cannot read what they have written. 



Inftead of the frame with parallel threads, I employ a board 

 which has feveral conveniences. 



This board is about 10 inches in breadth, and 16 high ; on A more conve- 

 the left fide, and near half an inch from the edge, there wajj^ JjjJ for 

 fmall dove-tailed groove from top to bottom. A rule three 

 quarters of an inch wide, and 4| long, Hides in this groove 

 by a piece fo formed as to fit the groove. Another rule five 

 eighths of an inch wide, is fixed perpendicularly to the firfl 

 rule in the form of a T, and ferves very conveniently to di- 

 rect the little finger of the hand that writes. Laftiy, the left 

 fide of the board is divided into notches almoft half an inch 

 diftant from each other : this being done, the following is the 

 method of writing : 



The paper is placed under the long rule, and is fattened by Method of wris- 

 two fcrews eafy to be imagined, which prefs it againft the in g with ink. 

 board : the writing is performed by keeping the hand lightly 

 over the rule, the little finger being behind. The rule is 

 fhifted from line to line very readily by the left hand, the 

 thumb being applied to feel the notches. At the finifh of 

 every line ink is dipped or taken (in a filver pen formed in the 

 ufual method) out of a broad flat veffel conftantly containing 

 ink to the depth of between one eighth and one quarter of an 

 inch. 



By this procefs, the lines may be written as near each other 

 as may be required. The rule directs the hand better than a 

 wire, which is too flexible, and not broad enough. When, 

 after difcontinuing writing the writer is defirous of proceed- 

 ing, the rule indicates the point to begin from, &c. 



* If the paper be rubbed with pumice, or have fome earthy 

 powder in the fize, and a blunt point of hard pewter be ufed, the 

 letters will be neat and vifible,—-N. 



INK 



