386 E. W. Brown — Apparatus for Tidal Analysis. 



Art. XXIII. — A Simple and Inexpensive Apparatus for 

 Tidal Analysis ; by Ernest W. Brown, F.R.S. 



The object of this paper is the description of an apparatus 

 for the analysis of tidal observations which anyone may quickly 

 construct for himself at an expenditure of a dollar or so. 

 Darwin's well-known apparatus* has disadvantages which he 

 himself recognized. It consisted of strips of xylonite on 

 which the observations were written, and of guide sheets care- 

 fully printed to show the positions in which the strips were to 

 be placed for the evaluation of any particular tide. He had 

 these made for a year's observations and about a dozen differ- 

 ent periods ; each sheet was to serve for 74 days and there 

 were thus some 60 large sheets to be used. 



The device described here is intended to obtain precisely the 

 same result as that of Darwin. The strips are replaced by 

 endless paper bands and the guide sheets by simple instructions 

 for arranging the bands and for testing the correctness of the 

 arrangements. The simplification is partly due to the intro- 

 duction of adding machines, now in practically universal use 

 where large masses of additions are to be performed. With 

 them it is no longer necessary that the digits should be very 

 accurately in column for easy addition ; so long as the com- 

 plete numbers are sufficiently nearly in a column as not to be 

 confused with numbers in a neighboring column, the operator 

 has no difficulty in following his work : with accurately ruled 

 paper, however, the numbers can be put into accurately placed 

 columns as easily as in Darwin's method. Nothing else in the 

 device requires any great care. As its successful use depends 

 mainly on small details, I have described the latter somewhat 

 fully. There is also another reason for this. Experience has 

 shown that a considerable proportion of the time of the opera- 

 tor is often taken up with the arrangement of his work, fre- 

 quently more than the actual calculation. There is thus more 

 opportunity for the saving of time and trouble and con- 

 sequently expense (which is now the chief factor in reducing 

 tidal observations) by the simplification of the arrangement of 

 the work, than in any other part of it. An apparently trifling 

 detail in operation may make the difference between success 

 and failure in this respect. 



The materials required are ruled paper, sheets of cardboard, 

 paper cutter, a few brads and double-pointed tacks, and a board. 



The ruled paper should be of good quality with smooth 

 finish and not so heavy as to prevent it from folding easily. 

 The horizontally and vertically ruled lines are to be uniformly 

 *Koy. Soc. Proc, A, vol. Hi, p. 345, 1892, Sc. Papers, vol. i, 216. 



