24 
HINTS TO TRAVELLERS. 
can be improvised out of a biscuit tin, or any vessel with vertical sides 
and an unobstructed mouth. Such a vessel standing level would collect 
the rain, the depth of which might be measured by an ordinary inch-rule. 
It is rare, however, to find rain so heavy as to give any appreciable depth 
when collected in a vessel freely open to evaporation, and in order to 
estimate the amount of rainfall to small fractions of an inch, the device is 
employed of measuring the water collected in the receiver of the gauge in 
a glass jar of much smaller diameter than the mouth of the collecting 
funnel. Thus, if the funnel exposes a surface of fifty square inches, and 
the measuring glass has a cross-section of one square inch, the fall of ^ 
of an inch of rain on the funnel will give a quantity of water sufficient to 
fill the measuring glass to the depth of an inch. In this way the actual 
rainfall may be read to the thousandth part of an inch without trouble. 
The smallest diameter for a serviceable rain-gauge is five inches, and this 
size is well adapted for the traveller. A three-inch rain-gauge might be 
employed, but the results obtained with it are not satisfactory. The rain- 
gauge should be placed in an open situation, so that it is not sheltered by any 
surrounding trees or buildings, and it ought to be firmly fixed by placing 
it between three wooden pegs driven securely into the ground. The 
mouth of the gauge should be level, and when the instrument is fixed, 
the rim of the funnel ought to be one foot above the ground. A spare 
measuring glass should be carried, but as there is always a consider¬ 
able risk of breaking such fragile objects, it is well to carry also one or 
two small brass measures of the capacity of half an inch, two-tenths of 
an inch, and one-tenth of an inch of measured rainfall. In this way, 
although no satisfactory record could be kept of light rainfall, a very fair 
estimate may be made of any torrential showers, the half-inch measure 
being used first, and then the smaller measures, finally estimating by eye 
the fraction of the tenth of an inch that remains over. It must, however, 
be distinctly borne in mind that an estimate formed in this way is not an 
accurate measurement, and the fact of using the rough method must be 
stated in the note-book. 
When snow falls along with rain, the melted snow is measured as 
equivalent to rainfall, and if the funnel of the rain-gauge should contain 
some unmelted snow at the time of observation, it should be warmed 
until the snow melts before a measurement is taken. If the receiving 
bottle of the rain-gauge should be broken by frost or accident, any other 
