64 An Improved Self-Registering Bain-Gauge. 



rain-gauge collector flows on its way to the vase. In this 

 receiver is a valve, which is ordinarily kept open by a small 

 counterpoised lever on the top of the tube, allowing the rain 

 to trickle unobstructed into the vase ; immediately, however, 

 the syphon commences to act, and it delivers the first drop 

 at the longer leg, the falling water depresses a small bucket 

 on the end of a lever, which pulls down the valve lever, to 

 which it is connected by a very light wire, and the valve at 

 once closes the tubular reservoir, allowing no more than 

 exactly the quarter of an inch to enter the vase until it is 

 quite empty, for as the last drop flows out the counter- 

 poised lever lifts both bucket and valve, and the small amount 

 accumulated while the syphon was acting is delivered into 

 the vase just as it comes back to zero. This syphon empties 

 the vase in nine seconds, and it must be evident with this 

 arrangement that the register will be as accurate as can well 

 be desired, and, I think, quite as accurate as necessary. 



There are two parts of this instrument I should like to say 

 a few words upon — the spiral springs and the hanging pen. 

 I find that Dr. Draper, of the New York Meteorological 

 Observatory, speaks most highly of the performance of 

 carefully made spiral springs of steel wire, for many pur- 

 poses of measurement in meteorology, and my own experience 

 entirely coincides with his. Spiral springs made of piano wire, 

 carefully wound on a turned and hollow iron mandril, evenly 

 hardened, and tempered at the temperature of burning oil 

 before removing from the mandril, appear to be perfectly 

 resilient, and some I have had in use for nearly three 

 years give the same results in weighing as when first 

 made. For delicate measures, of course, the spirals must 

 be long; the longer they are the more difficult it is to 

 harden and temper them properly, and it becomes neces- 

 sary to heat them for both processes inside of an iron tube, 

 which can be evenly heated throughout. I am about to 

 attempt making such spirals 18 inches long. The other 

 matter I wish to draw your attention to is the form of pen. 

 It is simply a piece of small glass tube, drawn down at one 

 end to a point with a fine capillary bore, and is very easily 

 made. This pen is fixed in a little wire holder, which hangs 

 on the gallows or frame like a small pendulum, with the pen 

 as its bob, and free to move backwards and forwards in a 

 vertical plane passing nearly through the axis of the barrel. 

 Its point is so adjusted that it rests against the paper with a 

 minimum of pressure and, therefore, with the smallest amount 



