78 G. H. HALLIGAN. 
this means the introduction of gearing for the reduction of 
the movement of the float. This gearing means friction, 
and the introduction of another element of error into the 
machine. On the coasts of Australasia the spring tides 
have a range of from five to about twelve feet, so that a 
reduction of about one-sixth meets all requirements, and 
if the clock-driven cylinder is made 24 inches in circum- 
ference, or one inch to one hour, a sheet of convenient 
size is obtained. 
The well known scientific instrument makers MM. 
Richard Freres of Paris, have designed a most useful 
gauge by means of which almost all these sources of error 
have been avoided, and the machine is especially of use to 
surveyors, or for purposes for which temporary gauges only 
are required. It consists of a metal case A (Plate 2), in 
which is arubber bag to which the water has access through 
holes in the case. A flexible brass or copper tube B, about 
°08 inch internal diameter, is connected with the rubber 
bag by means of a valve on the top of the case. The other 
end of the tube ends in a flexible box C, on the top of which 
is a rod, connected with the arm EH. This arm is pivoted 
at D and has, on one end a balance weight G, and on the 
other a pen or pencil H. The cylinder J is revolved by 
clockwork once in 24 hours. 
The rubber bag in the metal case has air pumped into it 
at such a pressure that the pencil H will rest at zero when 
the metal case is on its bed, a few feet below the lowest 
known tide. As the tide rises or falls it presses unequally - 
on the rubber bag, and this pressure is communicated 
through the copper tube B to the arm E and thence to the 
pencil H which traces a curve on the revolving cylinder J, 
the abscissee representing the heights and the ordinates the 
hours. It is a pity that in a machine so ingeniously 
designed and so simple in its working and so portable, it 
