April 19, 1900J 



NATURE 



591 



this being the first record of the genus south of the 

 equator in the Eastern Hemisphere— seven specimens 

 were taken, all, unfortunately, females. 



The results of this expedition are evidently such as 

 to encourage the Colonial Government in continuing the 

 work, as Mr. Waite has been able, not only to add to 

 scientific knowledge, but to obtain much information 

 directly bearing on the fisheries. If all of our Sea 

 Fishery Districts Committees were to combine in carry- 

 ing on similar operations round our own coast, notable 

 progress would be made towards obtaining that approxi- 

 mate " census" of our territorial waters which is required 

 for the solution of both scientific and econom.ic problems. 



W. A. Herdm.an. 



THE ORIGIN AND OCCURRENCE OF 

 CA VE-ICE. 



A LTHOUGH ice-caves and their phenomena present 

 ^^ some of the most interesting problems in the whole 

 range of physical geography, it is singular to note how 

 comparatively little attention has been directed to their 

 investigation, and how inadequate still is the sum total 

 of observation and experiment hitherto carried out, for 

 the full elucidation of the many questions which arise in 

 connection with their study. A recent investigator in 

 this field of research is Dr. Hans Lohmann, who, in an 

 admirable treatise on cave-ice ('' Das Hohleneis unter 

 besonderer Beriicksichtigung einiger Eishohlen des 

 Erzgebirges," Jena, 1895), has brought together the 

 results of previous work on the subject, and incorporated 

 an account of his own observations in the ice-caves of 

 Saxony. It is here only possible to set forth in the 

 merest outline some of the more interesting facts con- 

 nected with these natural ice-stores, and to indicate in 

 brief the theories that have been advanced to account 

 for some of their phenomena. 



Ice-caves have been defined as natural or artificial 

 cavities in the earth, in which ice, formed within them, is 

 preserved either the whole year round or for a greater 

 part of it. They may be roughly divided into two 

 classes, termed by Thury "static" and " dynamic," or, 

 according to Fugger, the ice-caves properly speaking 

 and the ''wind passages." The first are blind caves 

 with only a single outlet, while the caves of the second 

 class have connection by passage or cleft between their 

 inner end and the outside air at some point in the hill- 

 side higher than the main entrance. Almost all known 

 ice-caves are situated in the north temperate zone 

 (roughly, between 40^ and 6o~), and the few exceptions 

 which lie nearer the equator are so highly situated that 

 in winter the temperature within them falls below the 

 freezmg point. Generally speaking, the caves do not 

 lie in high mountain regions, though all are located 

 where snowfall is possible. 



The causes which bring about the formation of the 

 ice are to be looked for solely in the meteorological and 

 climatic conditions of the localities in which the caves 

 occur. In the case of blind caves, the floor of the cavity 

 is situated at a lower level than that of the entrance, and 

 when the outer atmosphere becomes cooled below the 

 temperature of the inner air, the former, by reason of its 

 greater density, sinks into the cave, slowly displacing the 

 contained air and thus giving rise to an air-current 

 which brings about the chilling of the cave. When the 

 outside temperature rises, that of the cave begins to rise 

 also, but only slowly at first, because the warmer outside 

 air possessing a smaller specific gravity can no longer 

 sink into the cave, and the heat is conducted to the 

 interior very slowly. During such periods (the "closed 

 periods" of Trouillet) a temperature curve, shown by a 

 registering thermometer placed within the cave, assumes 

 the form of an almost straight line. The inner temperature 



NO. 1590, VOL. 61 J 



then lingers for a long time in the neighbourhood of the 

 freezing point, but rises again with comparative rapidity 

 when all the contained ice is at last melted. 



The cold produced by evaporation within the cave also 

 tends to lower the temperature, and in those ice-caves 

 classed as " wind passages " the influence of evaporation 

 in this direction is very marked. While in summer the 

 air contained in the blind caves is perfectly still, a strong 

 air-current is found to prevail at this season in the wind- 

 passages. It has been observed that when the outer 

 temperature was considerably higher than that within, 

 the wind-stream was passing outwards ; at such time as 

 the inner and outer temperature were alike, the current 

 was intermittent or not observable ; but when the outer 

 temperature was lower than the inner, the draught was 

 passing inwards. In such cases we have two separate 

 air columns of equal height, one situated within the 

 mountain, the other formed by the outer atmosphere. 

 As soon as a difference of temperature in the two 

 columns is brought about, the tendency to restore equili- 

 brium gives rise to the air-current through the cave, as a 

 result of which the latter becomes cooled in the winter 

 and gradually warmed during the summer. But the 

 downward current which prevails in summer may some- 

 times bring about a considerable cooling within the cave 

 through evaporation, and if the outer air be very dry the 

 formation of ice may even take place. Systematic 

 observation has made it clear that the potent factor in 

 the production of ice within the caves is the air-current. 



The ice itself, formed principally during the spring-time, 

 when the conditions of temperature and water supply are 

 most favourable, is distributed in a varying manner ; it 

 may clothe the floor, the walls and the roof as a close- 

 fitting sheet, or may hang in curtain-like form from the 

 roof, or give rise to the formation of ice-stalactites and 

 stalagmites, according to the distribution and manner of 

 the water supply from above. 



In connection with the thawing of ice-stalactites, an 

 interesting phenomenon may sometimes be observed. 

 Since the collecting point of the drip which gave origin 

 to the stalactite is situated in the centre of the base of 

 the latter, the thawing action of the water from above 

 may proceed in such a way as to eat out the centre of 

 the stalactite, leaving its peripheral parts hanging as a 

 mere shell or tube. This has been explained by the fact 

 that the warmer water introduced, having a greater 

 specific gravity than water at the freezing point, will tend 

 to sink to the base of the little hollow formed at the root 

 of the stalactite as a first result of thawing, and thus 

 rapidly carry out its work as a vertical borer. 



But perhaps the most interesting phenomenon ex- 

 hibited by cave-ice, to the description and elucidation of 

 which Dr. Lohmann has devoted special attention, is the 

 peculiar structure known as the " prismatic " or " honey- 

 comb " structure. At certain times the surface of the ice 

 is found to be broken up by a net-like system of fine 

 crevices, resulting in the production of meshes of varying 

 and more or less irregular form. It has been found that, 

 strictly speaking, this structure does not appear during 

 the winter, nor does its formation occur in all cases at 

 the same time of the year. While in some caves this 

 splitting process has never been observed to take place 

 before the end of August, the ice in the caves of Saxony 

 have exhibited the structure in an advanced stage as 

 early as the month of March. The size of the meshes 

 is very variable, and they may reach dimensions so 

 great as 400 square centimetres, or be so minute as 

 to be observed with difficulty by the naked eye. The 

 crevices may be merely superficial, or may penetrate the 

 ice to a depth of several centimetres, there to cease 

 abruptly, and thus give rise to a superficial " prismatic 

 layer " sharply separated from the compact ice beneath. 

 But the development of honeycomb structure often pro- 

 ceeds so far that a thin ice-sheet is completely penetrated 



