20 Mr. Francis Gallon [Jan. 27, 



possible to draw any line that shall commend itself to the eye as 

 possessing more regularity than the image of a succession of dots or 

 cross strokes, 300 to the inch, when viewed at the distance of a foot. 

 Every design, however delicate, that can be drawn with a line of 

 uniform thickness by the best machine or the most consummate artist, 

 admits of being mimicked by the coarsest chain, when it is viewed at 

 such a distance that the angular length of each of its links shall not 

 exceed one minute of a degree. One of the apparently smoothest 

 outlines in nature is that of the horizon of the sea during ordinary 

 weather, although it is formed by waves. The slopes of debris down 

 the sides of distant mountains appear to sweep in beautifully smooth 

 curves, but on reaching those mountains and climbing up the debris, 

 the path may be exceedingly rough. 



The members of an audience sit at such various distances from the 

 lecture table and screen that it is not possible to illustrate as well as 

 is desirable the stages through which a row of dots appears to run 

 into a continuous line, as the angular distance between the dots is 

 lessened. I have, however, hung up chains and rows of beads of 

 various degrees of coarseness. Some of these will appear as pure 

 lines to all the audience ; others, whose coarseness of structure is 

 obvious to those who sit nearest, will seem to be pure lines when 

 viewed from the farthest seats. 



Although 300 dots to the inch are required to give the idea of 

 perfect continuity at the distance of one foot, it will shortly be seen 

 that a much smaller number suffices to suggest it. 



The cyclostyle, which is an instrument used for multiple writing, 

 makes about 140 dots to the inch. The style has a minute spur- 

 wheel or roller, instead of a point ; the writing is made on stencil 

 paper, whose surface is covered with a brittle glaze. This is per- 

 forated by the teeth of the spur-w 7 heel wherever they press against it. 

 The half perforated sheet is then laid on writing paper, and an inked 

 roller is worked over the glaze. The ink passes through the per- 

 forations and soaks through them on to the paper below ; consequently 

 the impression consists entirely of short and irregular cross bars or 

 dots. 



I exhibit on the screen a circular letter summoning a committee, 

 that was written by the cyclostyle. The writing seems beautifully 

 regular when the circular is photographically reduced ; when it ia. 

 enlarged, the discontinuity of the strokes becomes conspicuous. 

 Thus, I have enlarged the word the six times ; the dots can then be 

 easily seen and counted. There are 42 of them in the long stroke of 

 the letter h. 



The appearance of the work done by the cyclostyle would be 

 greatly improved if a fault in its mechanism could be removed, which 

 causes it to run with very unequal freedom in different directions. It 

 leaves an ugly, jagged mark wherever the direction of a line changes 

 suddenly. 



A much coarser representation of continuous lines is given by 



