522 REPORT—1890. 
In devising these automatic arrangements several difficulties presented 
themselves besides those inherent in all chronographic apparatus. Any- 
thing in the nature of standing apparatus was inadmissible, as it would 
interfere with the working and adjusting of the tanks. The apparatus 
must be such as could be put up and taken down with facility, and hence 
could not admit of complicated arrangements. A pencil worked direct 
by a float with a drum turning about a vertical axis by a clock, all to 
stand on the level glass surface, appeared the most desirable arrangement. 
In the first instance, a clock driving a detached vertical cylinder with a 
cord was kindly lent by Dr. Stirling from the Physiological Laboratory 
of Owens College, and an arrangement of float and stand was con- 
structed by Mr. Bamford. The loan of this clock was temporary, and 
experience gained with it led to the purchase of an ordinary Morse 
clock from Latimer, Clark, & Co. at comparatively small cost. A pulley 
was fitted so that the clock would drive the borrowed cylinder. This 
clock did its work quite as well as the more costly instrument. Its 
rate of action varied considerably with the resistance of the apparatus 
to be driven, so much so that the curves taken at different times from 
the same experiment could not be compared by superposition. Still, the 
action of the clock during the individual observations was sufficiently 
regular to give a fairly true tide curve, and it became obvious that it 
would be impossible to obtain any independent clock-driven apparatus 
that would give absolutely constant speeds such as would admit of the 
comparison of the curves taken from different parts of the estuary by 
direct superposition. To obtain such comparison it would be necessary 
to move the paper by the gearing which moved the generator. 
22. Compound Harmonic Tide Curves——On considering how best this 
might be done, it appeared thatif the paper had a horizontal motion - 
corresponding to the rise and fall of the generator while the pencil had a 
vertical motion corresponding to the rise and fall of the tide at any point 
in the tank, then if the tide were in the same phase as the generator the 
curve would be a straight line or an ellipse of infinite eccentricity with a 
slope (tan 6) equal to the rise of tide divided by the horizontal motion 
imparted to the paper, while any deviation of phase would be shown by 
the character of the ellipse or closed curve described by the pencil, and 
that to obtain the time-tidal curve from such curves would be easy by 
projecting on to a circle, while for the purpose of comparison and bringing 
out any difference of phase or deviation from the harmonic curves such 
compound harmonic curves would be much more definite than the harmonic 
curves. ‘This plan was therefore adopted with the happiest results, for, 
although it may take some study to become familiar with the curves, the 
obvious differences in these curves taken at different parts of the tanks 
and at the same part at different stages of the progress towards a state 
of equilibrium, together with the similarity of the curves taken in the 
two tanks or in different experiments at the corresponding places and 
corresponding numbers of tides run, including the final states of equili- 
brium. Plate XVIII. brings out more emphaticaliy than anything the in- 
terdependence of the character of the tide on the arrangement of the sand 
and the coincidence of a state of equilibrium of the sand with a particular 
tide curve at each part of the estuary. 
In these experiments the balance of the tanks has been adjusted so as 
to make the time intervals of rise and fall of the generator equal, .¢., to 
make the motion of the generator harmonic, so that these compound 
