642 



NATURE 



[Oct. 17, 1878 



5,703 feet, while on the other hand it has been placed as low as 

 4,300. It ij not probable that the height has altered during the 

 last century, for although some writers have asserted that the 

 mountain lost 503 feet during the eruption of 1845, it has been 

 satisfactorily proved that the crater of 1845 opened in the side 

 of the mountain below the principal craters. The previous 

 eruption was in 1772. Hekla is often spoken of as if it were the 

 only volcano in Iceland, while in reality the whole island is 

 dotted over with volcanic vents, of which Hekla is indeed the 

 most frequently active, but by no means the highest. In fact, 

 there are four higher mountains in the i-^land, the highest being 

 Oraefa JokuU — 6,426 Engli-h feet. 



Secondly, as to the shape of Hekla. Volcanoes often present 

 a fairly symmetrical conical form, as we should expect from 

 their mode of formation. This is specially the ca?e in regard to 

 Etna. But Hekla presents rather the appearance of a hog's 

 back. Seen from the north or south it has a long oval outline, 

 serrated by virtue of its three craters, and \\'\\Sx an axis which 

 passes from north-east to south-west. Thus the ends of the oval 

 mass alone present the usual conical appearance of volcanoes. 

 It is rather a line of craters than a single one ; a volcanic rift 

 elevated above the plain, with large bocche del fuoco. These 

 rifts are common in all volcanic countries. In Iceland we have a 

 notable example in Koetlagia, as we commonly call the volcano ; 

 in reality Koetla-gia — the Koetla rift, along the line of which 

 various vents of fire exist. So again we have Almannagja, the 

 great rift at Thingvellir. In the eruption of Etna, which took 

 place in 1865, a large rift opened in the side of the mountain, 

 and along the line of it no less than seven small craters opened. 

 In the last eruption of Hekla fourteen small craters opened in a 

 line. We have to distinguish between volcanoes terminated by 

 one large crater, which always furnishes the vent when the 

 eruption takes place from the summit, and volcanoes terminated 

 by a line of craters, one or other of which may be active at any 

 one time. To the former class belong Etna and Vesuvius, to 

 the latter Hekla and Koetla-gja. 



Apparently we cannot get cut of the way of spelling Hekla 

 Hecla. In one of our leading journals of 'October 11 I notice 

 the spelling Hecla. Hekla means hooded, in allusion to the 

 covering of snow, or of cloud, which so frequently rests upon 

 its summit. Hokull signifies a chasuble in Icelandic. Accord- 

 ing to some writers Mount Pilatus, near Lucerne, takes its 

 name from Pilcatus, in allusion to its cloud-capped summit. 



Marlborough College, October 13 G. F. Rodwell 



Animal Intelligence 



As many of the readers of Nature have probably not seen 

 iny article on the above subject in the current number of the 

 Nineteenth Century, I feel it desirable to repeat in these columns 

 the request with which that article concludes. This request is 

 merely that those who read it should favour me by sending to 

 the under-mentioned address brief accounts of any well-marked 

 instances of the display of animal intelligence which may have 

 fallen within their own notice or that of their friends. None of 

 these instances will be published by me without permission ; but 

 I desire to accumulate as many of such instances as possible — no 

 matter of how dubious a character — in order that I may obtain 

 a wide basis of suggestion as to the directions in which experi- 

 ments may be most profitably employed. I may add that as the 

 effect of publishing this invitation in the Nineteenth Century has 

 been that of burying my desks in a snow-storm of letters, I 

 should like to take this opportunity of explaining to past and 

 future correspondents that I do not esteem their kindness the less 

 because its bounty is too great for me to acknowledge in indi- 

 vidual cases. George J. Romanes 

 18, Cormvall Terrace, Regent's Park, N.W., October 15 



The Microphone as a Receiver 



I HAVE made some experiments which seem to throw light on 

 the fact mentioned by Prof. Hughes and also by Mr. Blyth 

 (Nature, vol. xviii. p. 172), that the microphone, or a jar with 

 gas cinders, may act as a receiver. 



A Morse-key is set on a sounding-box ; one pole of an inter- 

 mitting current is connected with the lever ; the other pole with 

 the fore-part of the key (which for telegraphing purposes is 

 connected with the positive pole of the sending battery). By 

 regulating the screw, which is found at the after-part of the 

 key (which for telegraphing purpDses is connected with the coil 



of the electro-magnet), a slight contact is made between the 

 lever and the fore-part of the key, and directly a very distinct 

 sound is heard of the same character as that of the sound 

 emitted by the interrupting apparatus. 



A very good form of the same experiment is the following : — 

 A leaden cylinder and a rocker are taken as used in the experi- 

 ment of Trevelyan ; the rocker is placed on the cylinder, and 

 is, moreover, supported by a sharp edge ; if necessary pressure 

 downwards is applied on the stem, in order to prevent the pres- 

 sure of the rocker on the cylinder being too gi-eat. The cylinder 

 is connected with one pole of the intermitting current, the stem 

 of the rocker with the other pole. If the pressure of the rocker 

 on the cylinder be regulated well, a very low sound is produced, 

 specially when the rocker is an iron one. A copper rocker or a 

 copper plate also gives good results. The cylinder was placed 

 on a sounding box. 



An intermitting current sent through the microphone of Prof. 

 Broun (Nature, vol. xviii. p. 383), as also through a jar with 

 gas cinders, gives a feeble though perfectly audible sound. By 

 using a stronger current, I believe the sound would have been 

 louder. My battery was of four Bunsen cells. 



In my opinion the only possible explanation of these facts is 

 the following : — The resistance at the places of contact being rela- 

 tively very great, a good part of the heat generated by the current 

 appears here, and by dilatations the lever of the Morse-key or 

 the rocker is uplifted. During the interruptions of the current 

 the heat is diffused, and the lever or the rocker falls back, to be 

 again uplifted in the next period of closed current. In this way 

 the lever or the rocker acquires an oscillation of the same period 

 as that of the intermitting current. That a sufficient diffusion 

 of heat in so short a time is possible may be seen from the 

 Trevelyan experiment itself. 



My conclusion is that the action of the microphone or of the 

 jar with gas cinders as a receiver depends upon the varying 

 dilatation at the points of contact by the varying intensity of the 

 current. V. A, JULIUS 



Breda, Holland, October 12 



Power of Stupefying Spiders possessed by Wasps. — 

 Mimicry in Birds 



Mr. Cecil's remarks on the spider-hunting wasp (Nature, 

 vol. xvii. p. 381) have interested me greatly, these wasps being 

 very common here. Two species are continually hovering 

 about the wall-plates and eaves of my house in search of their 

 prey, which they hunt out with most praiseworthy perseverance. 

 Both are thin -bodied, but one is half as long again and has a 

 larger body, as also broader black rings than the other. A 

 few remarks may be of interest to your readers. 



These wasps build variously-shaped mud nests, which are 

 met with hanging from twigs in the bush or stuck on walls in 

 houses and under overhanging rocks. Some species use a red 

 sandy loam, others common mud. 



The nest is divided into compartments, each of which con- 

 tains an ovum, and is filled with spiders, on which the larvae 

 feed. 



For a long time I was under the impression that these spiders 

 were killed outright, and was puzzled to find them perfectly 

 fresh and juicy after a lapse of a fortnight, with a thermometer 

 ranging up to 118° in the shade ; but a few days ago I broke 

 open a large nest, and was astonished to notice a constant 

 movement in the legs of half-a-dozen spiders which were con- 

 tained in one cell. 



. I have since then examined several nests, and invariably with 

 the same result. 



Mrs. Hubbard's explanation of the tracking described by Mr. 

 Cecil (Nature, vol. xvii. p. 402) is no doubt correct as far as 

 it goes, but the wasps here seem to "go in" for every and all 

 species of spiders, with only one exception. 



My house abounds with a podgy black spider having a bright 

 vermilion patch on the medial line of the body and two bright 

 spots above this patch. This insect is a most venomous 

 and dangerous neighbour ; its bite is highly poisonous and in- 

 flicts excruciating agony on the person or animal bitten. I 

 have seen a terrier succumb to its effects in eight hours, and 

 one young man went mad in 186S from the effects of a bite 

 received in the wrist. Several persons have been bitten here 

 during the last two years, and only the immediate use of ammonia 

 and spirits saved them from serious injury. This spider is care- 

 fully avoided by the wasp, who immediately retreats on disco- 

 vering that the occupant of a web belongs to this species. 



