264 

Southport, and now manufactured by Negretti and 
Zambra. The theory is to make use of a pen 
actuated directly by a rod rising with the float 
(G), the receiver emptying by means of a syphon of 
large bore (I) started by being dropped a little by 
the action of a trigger (K) set off by the float rod 
when the receiver is full, and reset automatically 
by the escaping water entering a lower cylinder. 
In its first form this instrument was troublesome, 
sometimes failing to discharge, sometimes dis- 
charging too soon, but these difficulties have now 
been overcome, and when it is in careful hands I 
know of no better recording gauge. It gives an 
exceedingly clear and steady trace, and is much 
more sensitive to light rain than the Standard 
Casella gauge, while its less frequent discharges 
and rapid emptying give great accuracy in ‘the 
case of heavy falls. The main drawback is the 
employment ‘of mercury in connection with the 
syphon. 
The Fernley recording gauge (Fig. 3), also con- 
structed by Messrs. Negretti and Zambra, is the 
most recent product of Mr. Baxendell’s ingenuity, 
and I have had it under observation along with the 
Casella and Halliwell gauges at Camden Square 
for six months. The record it produces is as clear 
and sensitive as that of the Halliwell gauge, from 
which it differs only in the simpler method of 
starting the large-bore syphon, avoiding the use 
of mercury. This is accomplished by the inter- 
position of a small tipping bucket (H) filled with 
water. The bucket is tipped by a trigger actuated 
as in the Halliwell gauge, and discharges into the 
lower part (E) of the long leg of the syphon, which 
is started by the water pump action thus set up. 
The mechanism is certainly simpler than that of 
the Halliwell gauge, and the action is perhaps 
more certain than that of the first form of Halli- 
well. The principle is sound, and was employed 
in Osler’s famous recording gauge of 1837. 
The difficulty presented by all accurate recording 
instruments of different types is to ensure com- 
parability, so that regional variations in duration 
fee intensity may be worked out. To insist on 
the use of one make of instrument would hamper 
progress and discourage that competition between 
inventors and instrument makers on which so 
much depends for the progressive improvement of 
practical details. As the result of many years’ 
experience I have formulated the requirements of 
a satisfactory recording rain gauge for general 
use, as follows :— ‘ 
(1) A recording rain gauge is not a labour- 
saving contrivance which will work by itself for 
a week or more. The time scale should be so 
open that a drum of reasonable size cannot include 
more than the record of twenty-four hours, and 
it must be visited daily and the pen set to the 
correct time every morning. 
(2) If a recording rain gauge is to be generally 
adopted its price must be less than tol., sub- 
stantially so if possible, hence great size and 
elaborate mechanism must be avoided. 
(3) The depth scale must be magnified at least 
four, and preferably eight times, and to avoid the 
NO. VOL. 95] 
9245 
= 9)// 20 
NATURE 

[May 6, 1915 
inconvenience of having a very high drum some 
mechanical arrangement must be made by which 
the pen, on reaching the end of the chart, returns 
to zero automatically. 
(4) The usual method of bringing the pen back 
to zero by emptying the receiver when half an 
inch or less of rain has been accumulated neces- 
sitates the use of uncertain or complicated mech- 
anism, hence the receiver should be large enough 
to contain at least four inches of rain, and the 
automatic return of the pen should be secured by 
some device unconnected with the discharge. 
(5) Friction is the only other serious practical 
difficulty, and this should be minimised by having 
as few moving parts as possible and these with 
the shortest bearings compatible with rigidity. 
It was in order to meet these views that Messrs. 
Casella introduced their modification of their old 
standard recording gauge, but though most of the 
conditions were com- 
plied with, No. 4 
was not. The Hyeto- 
graph (Fig. 4) devised 
at the same time by 
Negretti and Zambra, 
carries out my views 
more nearly than any 
other gauge I -know; 
but it has not quite 
overcome the difficulty 
of friction in the float 
chamber, though when 
signs of this appear 
a very slight adjust- 
ment puts things 
right. Its curve also 
presents the  incon- 
venience common _ to 
those of the ordinary 
barograph and thermo- 



graph of being re- 
ferable to a_ straight 
co-ordinate for time 
and to the arc of a 
circle for amount. 
Its advantages are 
Laie) emecelver 
takes four inches of 
rain without overflowing, an amount which, 
it is true, may be exceeded in twenty-four 
hours in any part of the country, but which cannot 
be expected to be exceeded twice in a lifetime 
at the same place. It is emptied by a syphon 
actuated by suddenly depressing the float by hand, 
and should be so emptied each morning when the 
amount collected exceeds a small fraction of an 
inch. The pen drops on reaching the top of the 
chart by the edge of a plate fixed on the pen lever 
dropping from a peg (F) on the float rod (E) on to 
another peg below, an oil brake (M) at the short 
end of the lever (G) absorbing the shock. The 
record is thus not interrupted so long as rain is 
falling. During snow, a night-light placed in the 
instrument under the funnel ensures instantane- 

Fic. 4.—Section of Hyetograph. 
; Ous melting. 

