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



both horizontally and vertically, and the results used for the 

 analysis of the solar and long-period tides. 



For this and future arrangements, the number of the day is 

 written in red ink twice on each line in any one of the unoccu- 

 pied squares, once between the left edge and the observation for 

 ll h and once between the observation for ll h and 23 h . A pair 

 of single red lines is ruled so as to enclose all the observations 

 at h and a pair of double red lines to enclose all those at 12 b . 



The observations have now to be regrouped so as to give an 

 analysis for mean lunar time. For this purpose the first sheet 

 is placed face down on the table and the two edges folded over 

 so that the left edge comes on to the ruled line following the 

 observations at 23 h . It is pasted in this position by using the 

 inch overlap ; care being taken that the inside portions of the 

 paper do not stick together; the position of the folds is imma- 

 terial. The folded sheet is then placed on the paper cutter 

 and each day of observations is cut off ; it will form a closed 

 band. The first 37 of these bands are placed in order on the 

 paper cover, previously made, by bending the cover in one 

 hand and slipping the bands on with the other. The cover 

 carrying the bands is then flattened out and the sheet of card- 

 board bent and slipped in. The remaining 9 cards each carry- 

 ing 37 days of observations are treated in the same manner. 

 Thus the whole year's observations are contained on bands 

 stretched over ten cards. 



The bands have now to be arranged in accordance with a 

 scheme made out in advance. Suppose that the arrangement 

 required is such that the observations at the following times 

 are to be brought into the same column : d , h ; l d , l h ; 2 d , 2 h ; 

 3 d , 3 h ; 4 d , 4 h ; 5 d , 4 h ; and so on. The first card with cover and 

 bands is bent and the edges placed between the brads on the 

 board, care being taken that a band does not rest on the tacks. 

 Any band is then easily movable round the card ; it can be rapidly 

 and certainly brought into any position by gently pressing on 

 it with a piece of soft red rubber and sliding it to the right as 

 required.* If the band be pinched over the edge of the card 

 when it is brought into position it will remain there while the 

 other bands are being placed. The card and cover being about 

 12" long and the sum of the widths of the 37 bands being only 9". 

 25, there is ample room for the movement of the bands, it being 

 not necessary that they should lie very close to one another, f 

 The remaining 9 cards being treated in the same way 5 the 

 observations are ready for the summing which gives the M 

 series of tides. 



*If slid to the left there may be trouble owing to the inside pasted edges 

 of the band catching on the edge of the cover. 



f If the covers be made of fairly stiff paper, the cards and the board may 

 be dispensed with and the bands moved by one hand while the other holds 

 the cover. But this method is not quite so convenient for use. 



