606 REPORT — 1884. 



from Madras on the Bay of Bengal to Bombay on the Arabian Sea will give an 

 average maxium difference on quiet days of 7 volts ; between Bellary and Belgaum, 

 two inland stations east and west, 200 miles, an average of 2 or 2£ volts ; between 

 Belgaum and Vingurla, a station inland and one on the sea coast, seventy miles, an 

 average of 23 volts. Perhaps ]00 or 150 volts might be expected as the maxium 

 obtainable at the widest limits on the earth's surface on quiet days. It has not 

 always been possible to measure the potential difference occurring iu so-called 

 ' magnetic storms,' but 30 volts per 200 miles is not uncommon. 



As recent years have taught with what minute currents speech and telegraphic 

 svmbols can be transmitted over long distances, the author suggests that the 

 time may be coming when these earth currents shall be made of service for such 

 purposes, and telegraphy shall in general benefit. 



It is found on disturbed days that actual reversals of the earth's currents take 

 place in a few minutes ; but that, certainly within a range of 900 miles, these 

 reversals all agree on different lines; that is, all places east are positive or negative, 

 at the same time, and places west of the opposite sign simultaneously ; a large area 

 is affected at the same time and in the same way. Great throbs are felt, which 

 increase or decrease the currents in all lines together like the beating of the pulses 

 ■of the body. 



Seein°- that during the passage of sunspots, the obscured portion of the earth's 

 surface is said to cease to receive heat, it may be conjectured that there will be 

 consequent inequalities in the normal causes of difference of potential, sufficient to 

 account for the strong currents, so inimical to telegraphy. Such phenomena need 

 not discountenance the theory above set forth. 



16. Description of a Cylindrical Slide Bide or Calculating Apparatus. 



By Edwin Thacher. 



This apparatus consists of twenty separate bars united in a frame which is 

 movable about a cylinder. The bars present in sections printed logarithmic scales 

 of sixty feet, and of thirty feet radii. These bars read into the cylinder upon 

 which are printed two logarithmic scales of thirty feet radiu3 each. In this appar- 

 atus the bars form slides and are worked similarly to the ordinary slide rule, the 

 open divisions of the scales giving five places of figures instead of two as in the 

 ordinary rules. This rule performs with facility the solution of any question in 

 multiplication, division, and proportion of numbers, either simple or fractional, with 

 or without powers and roots. 



17 On the Inconveniences of the present Mode of quoting Scientific Journals. 



By Dr. H. Borns, F.C.S. 



The author called attention to the inconveniences arising from the injudicious 

 And arbitrary modes of quoting in use, and suggested that: — 1. Every Journal 

 should bear its abridged title by which it is to be quoted on the title page, in a 

 prominent position. 2. That all quotations should use, if necessary, the full title, 

 or these abridged titles with place, year, volume and page. 



18. An Account of unusual coloured Boivs observed in Fogs. 

 By Philip Bdrton. 



It is well known that a luminous biiw is sometimes formed in fogs by the 

 refraction and reflection of light in the particles of which they are composed. This 

 appearance, though sometimes nearly equal in size to the rainbow, is often perceptibly 

 smaller • and it differs from the latter also in not exhibiting any coloured rings, the 

 various colours being blended into a uniform whitish arch. 



Besides the ordinary fog-bow which can frequently be seen, a fainter or super- 

 numerary one may also be observed on rare occasions. This bow is smaller than 



