An Improved Self-Registering Rain-Gauge. 63 



until a quarter of an inch of rain had fallen, when an inter- 

 mittent syphon within the vase overflowed with the last 

 drop or two of the arranged amount, emptying the vase in a 

 few seconds, which gradually rose to its zero position. In 

 descending, the vase raised a light pen frame, carried between 

 vertical guide wires ; a glass pen, charged with aniline and 

 glycerine ink, being suspended like a pendulum in the frame, 

 marked on paper stretched on a cylinder revolving on a 

 vertical axis once in 24 hours every movement of the vase, 

 thus furnishing a graphic record of the time, intensity, and 

 duration of rainfall in a very reliable and satisfactory 

 manner. 



One point which appeared open to improvement was the 

 mode of communicating to the pen the movements of the 

 vase, which was done by a fine platinum wire passing up- 

 wards from the top of the vase over two delicate pulleys 

 downwards to the pen frame ; both pulleys and wire guides 

 produced sufficient friction to interfere somewhat with the 

 ultimate accuracy of the quantity register. The other direction 

 in which improvement was required was indicated by the fact 

 that the syphon took a very sensible interval to empty the 

 vase — say from fifteen to twenty seconds — and that in this in- 

 terval in heavy rains an appreciable amount of rain might 

 flow into the vase which would overflow with the rest with- 

 out giving any indication on the register that more than a 

 quarter of an inch had fallen. This defect, of course, would not 

 be very appreciable except in heavy rains; still it is in heavy 

 rains that the most accurate measures of intensity of fall are 

 required, and, therefore, a practical method of meeting this 

 difficulty was wanted. 



The new instrument — ombrograph, as it may be styled — is 

 on the table at work, and you can see the action, and also how 

 the defects I have referred to have been met. In the first 

 place, the pen is suspended from a little gallows on the vase 

 itself, any movement of which is recorded directly on the 

 cylinder without intervention of pulleys ; to prevent the 

 swinging to which a weight hung by spiral springs is very 

 liable to, the vase has two vertical ribs of thin metal, which 

 run loosely in two grooved guide wheels, running on fine steel 

 axles, by which contrivance a steady vertical movement 

 downwards and upwards of the vase, and therefore of the 

 pen, is secured. 



In the second place, a simple little intermediate tubular 

 receiver has been added, into which the water from the 



