February 19, 1903] 



NA TURE 



379 



This apparently close connection between solar promin- 

 ences and magnetic storms perhaps explains why it is that 

 the latter sometimes take place when there are no spots, 

 or no very large spots on the solar surface. Thus, for 

 instance, there may be prominences and magnetic storms 

 when there are no spots ; prominences may also sometimes 

 b? associated with large spots, and as the latter can be seen 

 while the former cannot, the resulting magnetic storm is 

 generally attributed to the spots. 



Further, the magnitude of magnetic storms appears to 

 vary according to the particular position as to latitude of 

 the prominence on the sun's disc. The nearer the poles 

 {either north or south) the prominence occurs, and these 

 are the regions where no spots exist, the greater the mag- 

 netic storm. 



In conclusion, it may be stated that the inquiry has shown 

 that the variations of the general magnetic phenomena, as 

 given by Ellis, synchronise with the occurrence of promin- 

 ences about the solar equator, while his " great " magnetic 

 disturbances occur, in point of time, with the appearance of 

 prominences in the polar regions of the sun. Prof. Bigelow 

 has recently (U.S. Monthly Weather Review, July, 

 1902, p. 352) investigated the variations in the horizontal 

 magnetic force, and finds that the curve representing these 

 changes exhibits subsidiary maxima which synchronise with 

 those recorded in the curve representing the mean variation 

 of prominences for all latitudes. Thus, to use his own 

 words, " the remarkable synchronism between the curves 

 cannot escape recognition, except after the year 1894, when 

 an extra minor crest is developed in the horizontal force." 



William J. S. Lockyer. 



THE FORTRESS OF THE MOLE. 



L70R the last three-quarters of a century, at any rate, 

 natural history writers have been content to copy a 

 diagrammatic figure of the breeding-hillock of the mole, 

 without the least attempt to ascertain for themselves to what 

 extent it is based on actual fact. The diagram in question 

 was based on a fairly authentic account of the mole's habits 

 drawn up by de Vaux just a century ago, but was elabor- 

 ated by G. St. Hilaire and further " improved " by Blasius. 

 Recently, Mr. L. E. Adams, whose special study is the 

 Mollusca, has examined a large series of mole-hillocks in 

 Staffordshire and has found that in no case does the struc- 

 ture of the one in which the nest is formed correspond with 

 the current diagram of the so-called "fortress." His 

 account, illustrated with numerous diagrams (two of which 

 we are enabled to reproduce) is published in vol. xlvii.. No. 

 4, of the Memoirs of the Manchester Literary and Philo- 

 sophical Society. It shows that in certain other respects 

 our ideas of the life-history of the mole require modification. 



With regard to the situation of the breeding-hillock, or 

 fortress, as it still may be conveniently called, Mr. Adams 

 finds that this is generally in the open field, although it 

 may occasionally be placed in a hedge-bank, but only when 

 there is a ditch alongside. Indeed, the proximity of water 

 seems to be the main factor in determining the position of 

 the structure. Now and then a fortress may be found under 

 a tree, but it is considered by the author that such a position 

 is probably accidental. 



According to the old idea, it was supposed that the runs 

 with which it is permeated were made on a certain definite 

 plan, allowing of free escape from the invasions of foes both 

 above and below ground. This idea receives no support 

 from the new observations, which tend to show that the 

 more or less complicated galleries are purely incidental, 

 and, with the exception of one " bolt-hole," have no refer- 

 ence to premeditated escape. In place, indeed, of being ex- 

 amples of a wonderful instinct of self-preservation on the 

 part of their constructor, it appears that the galleries of the 

 fortress are the natural, incidental and inevitable outcome 

 of the work of excavating the nest-cavity and piling up 

 the superincumbent mound. 



When the site for the fortress has been fixed, a circular 

 cavity is excavated for the reception of the nest at a depth 

 of from two to six inches below the surface of the ground, 

 except in the case of boggy soil or in situations liable to be 

 flooded, when the nest is often made above the original 



NO. 1738, VOL. 67] 



ground-level. The easiest way to dispose of the excavated 

 soil is to push it up to the surface, and for this purpose a 

 tunnel is constructed, and in such a case the whole mound 

 is made by this tunnel. 



"When this superincumbent earth," writes the author, 

 " has reached an inconvenient height, another tunnel is 

 made, sometimes from another part of the nest-cavity (Fig. 

 1, a, b), but more often sideways from the first upward 

 tunnel. All this takes time, and the mole meanwhile makes 

 fresh runs from the fortress, the seat of its labour, in various 



Fig. 1. — Plan of a simple mole fortress, from above, a, b, excavation 

 tunnels ; c , d, tunnels made for forming protecting heap ; n, nest. 



directions in search of food. Much of the earth displaced 

 in making these fresh runs falls' into the nest-cavity, arid 

 has to be disposed of in the same way as before, and also 

 the soil displaced in making the bolt-run and the down- 

 shaft, when this latter occurs. Now the tunnel (or tunnels) 

 leading upwards from the nest-cavity becomes larger and 

 larger, winding round under the surface of the growing 

 fortress. When this removal of earth becomes too fatiguing, 

 on account of the length of the tunnel, the mole will often 

 begin to make new tunnels from runs close to the end of the 



Fig. 



-A complicated mole-foi tress with eleven exits 



tunnels ; n, nest. 



<r, apex of the 



fortress. Sometimes these new runs break into those lead- 

 ing from the nest-cavity, but not very often ; usually they 

 lie above them." 



It thus appears that the tunnels are for two distinct pur- 

 poses. First, we have those formed for ejecting earth from 

 the nest-cavity and bolt-run, which are generally in the 

 shape of a corkscrew ascending from the nest, and often 

 with blind divergent terminations. And, secondly, tunnels 



