30 KEPORT 1870, 



demagnetization of tlie line-wire follows mucli more rapidly, the secondary cur- 

 rent is more intense, and consequently these coils more often suffer. 



When a circuit protected by the " lightning-bridge " is struck, the lightning 

 finds in its direct path not a space of air, but a bridge of conducting particles in 

 very close proximity to one another: it connects these imder the influence of the 

 discharge, and renders the pai-ticles highly incandescent. Incandescent matter, as 

 already demonstrated, oilers a very free passage to electricity, and the second«ary 

 current finds an easier passage across the heated matter than through the coils. 

 These lightning-bridges have been in use more than four years ; there are upwards 

 of 1000 doing duty in this coimtry alone, and not a single case has occurred of a 

 coil being fused when protected by them. 



Four years have elapsed since the introduction by the author of induced mag- 

 netic needles for needle telegi-aphs ; there are some thousands of them now doing 

 daily work. The coils of the old pattern are being converted into induced magnet 

 coils, and it is probable that induced magnet coils vrill entirely supersede the so- 

 called permanent magnets used in needle-telegraph instnmients. 



Meteoeology. 



BainfaJl — its Variation %vit7i Elevation of the Gauge, 

 By Charles Chambee.s, F.R.S. 



The fact is well known to meteorologists that the quantities of rain received in 

 gauges placed at difl'erent heights above the ground diminish as the elevation of 

 the gauge increases. Several attempts have been made to explain this phenome- 

 non, but none of them are so satisfactoiy as to discourage the search for other 

 causes that may contribute substantiallv or mainly to its production. Hence the 

 submission for the consideration of the liritish Association of this further attempt. 



One of the principal causes of rain is imdoubtedly the transfer, effected by winds, 

 of air charged vrith moisture in a wann damp district to a colder region, where the 

 vapour it contains is partially condensed. The temperature of the lower as well 

 as of the higher horizontal strata of the atmosphere oeiug reduced by this transfer, 

 it may fairly be inferred that condensation of vapour may also occur in the lower 

 as well as the higher strata. The rain caught by a gauge at any given elevation 

 will therefore be the sum of the condensations in all the strata above it, and thus 

 the lower a gauge be placed, the greater will be the quantity of rain received by it. 



Again, it is known by obsers'ation that there is at all times a greater or less dif- 

 ference of electrical tension between the atmosphere and the surface of the ground. 

 If, then (in accordance with the views of Prof. Andi'ews as to the continuity of the. 

 liquid and gaseous states of matter, from which it follows that the changes of 

 other physical properties must also be continuous), we regard the particles of vapour 

 suspended in the air as electric bodies in relation to the dielectric principal con- 

 stituents of the atmosphere, they 'will be polarized b}^ induction from the electricity 

 of the ground. This polarization will give rise to an attraction between every 

 particle and the neighbouring particles above and below it ; and being stronger in the 

 particles nearer the ground than in those more remote, the tendency of the particles 

 to coalesce (which will increase, by their mutual induction, as two neighbours 

 approach each other) will be greatest near the gi'ound. Thus it may be (each 

 particle gathering to itself its neighbours successively till their united density 

 exceeds that of the atmosphere generally) that some rain-drops are formed, and 

 that in greatest abundance, near the ground. If this be the true cause of any sub- 

 stantial part of the phenomenon in question, then as the variation of intensity of 

 electrical polarization of the particles will vary with height most rapidly near the 

 ground, so the variation in the rainfall near the ground should be more rapid than 

 at a gi-eater elevation ; and such is, indeed, the fact. Also, if the idea be coiTect, it 

 will probably serve to explain other phenomena which it was not specially conceived 

 to meet ; and so it does. For, first, it requires that the rainfall over even ground, 

 where the electrical tension is relatively weak, should be less than over similarly 



