504 



NATURE 



[Sept. 25, 1879 



m 



dora, and it is found that where telephones alone are useless be- 

 cause of the induction of adjacent wires, the instrument acts 

 admirably. The undulatory current produced by sonorous vibra- 

 tions is so intense that a person speaking about a foot away from 

 a transmitter has been heard ten feet from an ordinary telephone 

 in Manchester thirty-six miles a«ay by wire, and this although 

 the induction fro n some thirty adjacent wires had to be over- 

 come, and we may add that the intensity of the sound may be 

 largely augmented by employing increased battery power. 



Four carbon pencils are nicely centred and loosely held in 

 four blocks of carbin, abed; two opposite blocks, a and c, are 

 connected in circuit with a battery and the primary wire of an 

 induction-coil. The efficiency of the arrangement is now made 

 complete by having a telephone in the secondary circuit. The 

 carbon blocks are mounted on a thin wooden diaphragm, and 

 consequently are not seen in Fig. 3, which represents one form 

 of the finished instrument. 



For some months past an interesting and highly successful 

 operation has bean made every Sunday. One of these trans- 



Fig. 3. 



mitters is fixed in the pulpit of one of the Halifax places of 

 worship. Its position is not over-favourable, being half hidden 

 so as to escape attention, and thus to some extent its efficiency 

 is interfered with. In the nether regions, where the organ- 

 blowing apparatus is found, a Clamond's thermo-electric pile is 

 placed, and one of the first dutie-; of the sexton on a .Sunday 

 morning and evening is to light a gas jet under the pile. In this 

 way a sufficient supply of electricity is obtained to work exceed- 

 ingly well at a cost of less than 2d. per Sunday in gas consumed. 

 On the outskirts of the town Sf veral houses have telephones in 

 the secondary circuit, one of these belonging to an invalided 

 lady, and the service, from the opening voluntary to the parting 

 benediction, is heard plainly by every one. The rendering of 

 the music is especially fine, sounding to the observer, sat at 

 ease in an arm-chair, as if proceeding from a neighbouring room 

 with the door slightly ajar. 



William Ackroyd 



Colour-Blindness 



When your able reviewer Prof. Pole so plainly intimates, in 

 Nature, vol. xx, pp. 477 to 480, that he does not consider any 

 of the theories of colour-blindness he has mentioned to be alto- 

 gether sufficient for the observed facts, and that he may return 

 to the subject in a future number, I tru«t he may then take some 

 notice of my views, as honoured by the Royal Society, Edin- 

 burgh, in vol. xxviii. of their Transactions. 



At all events, it is much to be hoped that in his own future de- 

 scriptions, he will define his colours more accurately than by t'l'i 

 naked eye estimations and names of even those who are allov, eti 

 to possess normal vision. For, as I have shown in the pa hj- 

 above alluded to, there are physical distinctions, amounting to 

 more than the oppositions of black and white, and reacting <;n 

 colour, between many pigments generally reputed by the wo Id 

 to be all of the same colour to the eye. 



To speak therefore of green, or red, or brown is nothing ; but 

 it is what green, and what red, and what brown that must be 

 settled, as a preliminary to any further safe observation on the 

 subject. PiAzzi Smyth 



15, Royal Terrace, Edinburgh, September 19 



The Carving of Valleys ,^ 



In the course of a recent visit to Loch Maree, I observed an 

 interesting geological phenomenon in a glen on the east side of 

 the loch, which is traversed in ascending Ben Slioch, from 

 Kinlochewe, and which is called, I understand. Glen Beansdile. 

 This glen, in its lower part at least, follows the line of division 

 between the "fundamental gneiss," which rises in a gradual 

 slope on the north side, and the "Cambrian sandstone," which 

 on the south side forms a fine cliff, terminating at the base in a 

 long steep "debris line." The stream, which is of considerable 

 size, originally ran close to the foot of this cliff until it reached 

 the wide valley which contains the loch ; but at some peri id a 

 large "bergfall" of rocks from the sandstone cliff has dammed 

 up the ori;(inal bed, and diverted the stream into a new course, 

 diagonally across the gentle slopes of gneiss, which previously 

 formed the north side of the glen. This new course is marked, 

 first, by a small depression or gully in the &o\v of the glen, raid 

 secondly, in the middle of this, by a narrow ravine with vertical 

 sides, just wide enough to contain the stream which foams at the 

 bottom. 



There is nothing in itself very remarkable about this diversion 

 of a stream ; but the point which gives the case its interest is 

 that an inferior limit can be fixed for the time at which the 

 diversion took place. For, on descending into the secondary 

 depression above mentioned, I was able to trace the glaciation, 

 or planing down by ice of the edges of the gneiss (which was 

 admirably clear on these slopes) right down to the brink of the 

 little ravine containing the stream, thus showing conclusivel)- 

 that the diversion had taken place before the glacial period, and 

 so long before that the stream had time to cut a channel sufficient 

 to guide the glacier in its flow, and divert it from the work it 

 would otherwise have accomplished in clearing away the remains 

 of the berg-fall, and re-opening the old river-course. Thus it 

 will be seen that in the new channel we have an example of the 

 work which can be done by a mountain stream during a period 

 dating back at least beyond the glacial epoch ; while the old 

 channel exemplifies the work done in the same time by the various 

 agencies of " sub-aerial waste " — rain, wind, frost, &c. — with- 

 out a stream to assist them, either by direct erosion of its owa 

 or by sweeping away the dibris which they had brought down. 



What, then, are the phenomena presented by these two cases? 

 In the first, the only work which can really be ascribed to the 

 stream is the cutting of the deep narrow gorge at the bottom of 

 which it now runs ; for with regard to the vrider depression 

 above (itself a mere furrow in the main flow of the glen), it is 

 impossible to say how much has been due to the planing action 

 of the ice. In the second, the bottom of the old channel, if 

 there be any power in " sub-aerial waste," should be choked by 

 the dShris which has come down from its sides, whereas I was 

 easily able to detect live rock within a few feet of the tiny runnel 

 which now drains the gully, and which itself picks its way among 

 stones and boulders that are clearly nothing but the cumbered 

 bed of the old-world torrent. 



The question I wish to ask is whether the study of these two 

 examples is not sufficient to produce something like a conviction 

 that the modern school of geologists (as worthily represented by 



