THE TIDES 311 



tables of the times and heights of high water and low water 

 for fourteen of the Indian ports. 



To predict the tides for the India and China Seas and 

 Australia we have a much more difficult thing to do than for 

 the British ports. The Admiralty Tide Tables give all 

 that is necessary for the British ports, practically speaking; 

 but for other parts of the world generally the diurnal tide 

 comes so much into play that we have exceedingly compli- 

 cated action. The most complete thing would be a table 

 showing the height of the water every hour of the twenty- 

 four. No one has yet ventured to do that generally for all 

 parts of the world; but for the comparatively complicated 

 tides of the India Seas, the curves traced by the Tide Pre- 

 dictor from which is obtained the information given in these 

 Indian tide tables, do actually tell the height of the water 

 for every instant of the twenty-four hours. 



The mechanical method which I have utilised in this 

 machine is primarily due to the Rev. F. Bashforth who, in 

 1845, when he was a Bachelor of Arts and Fellow of St. 

 John's College, Cambridge, described it to Section A of the 

 1845 (Cambridge) meeting of the British Association in a 

 communication entitled " A Description of a Machine for 

 finding the Numerical Roots of Equations and tracing a 

 Variety of Useful Curves," of which a short notice ap- 

 pears in the British Association Report for that year. The 

 same subject was taken up by Mr. Russell in a communica- 

 tion to the Royal Society in 1869, " On the Mechanical 

 Description of Curves/'* which contains a drawing showing 

 mechanism substantially the same as that of the Tide Pre- 

 dictor. Here is the principal as embodied in No. 3 Tide 

 Predictor (represented in FIG. 133, p. 310), now actually 

 before you: 



A long cord of which one end is held fixed passes ov. 

 one pulley, under another, and so on. These eleven pulleyv 

 are all moved up and down by cranks, and each pulley takes 

 in or lets out cord according to the direction in which it 

 moves. These cranks are all moved by trains of wheels 

 gearing into the eleven wheels fixed on this driving shaft 

 The greatest number of teeth on any wheel is 802 engaging 

 *Proc. Royal Society, June 17, 1869; (vol. xviii. p. 72). 



