TRANSACTIONS OF THE SECTIONS. 89 



0)1 a Diagram of the Earth's Eccentricity and the Precession of the Equinoxes, 

 illustrating their Relation to Geological Climate ami the Rate of Organic 

 Chatige. By Alfeed R, Wallace, F.R.G.S. 



Tlie author exhibited a diagram of the eccentricity of the earth's orbit and the 

 precession of the equinoxes, from which he deduced certain important views as to 

 the climatesof past geological ages and the changes of organic life. During the 

 past three million yeai-s the eccentricity has been almost always much greater than 

 at present, on the average twice as great, and for long periods more than three 

 times as great. It was shown that when the eccentricity was greatest the heat 

 receiA'ed from the sun at the greatest and least distances w?s as 3 to 4 ; and, owing 

 to the precession of the equinoxes, the winters of the northern hemisphere would 

 be rendered intensely cold and much longer for periods of 10,500 years, while 

 during the alternate periods the winters would be mild and short, the summers cool 

 and long, leading to an almost perpetual spring. We thus have cold or glacial 

 epochs for about 10,000 years, alternating with mild epochs for the same period, 

 whenever the eccentricity was high, and this was the case for fully the half of the 

 last three million years ; and, as such alternations must have occiu-red during every 

 glacial epoch, the fact of intercalated warm periods and the migrations con- 

 sequent on them, which have been detected by geologists, must be looked upon 

 as the normal condition of things. But during the last 60,000 years (probably the 

 whole time elapsed since the close of the last glacial epoch) the eccentricity has 

 been very small, and the alternations of climate and consequent migi-ations very 

 slight ; and as Mr. Darwin holds that alternations of climate are, by means of the 

 consequent migrations, the most powerful cause of modifications of species, there 

 must have been a comparative stability of species durin» that period of time, from 

 which alone we obtam our idea of the rate of specific change. This idea will 

 therefore be eiToneous ; and the rate of change during past geological ages may have 

 been, and probably was, much more rapid than has hitherto been thought possible. 

 During three million years before and one million after the recent epoch, no less 

 than 130 alternations of climate occurred (each of 10,000 years' duration), when the 

 eccentricity was more than double what it is now ; and these incessant changes were 

 thought, on Dai-winian principles, to supply a vera causa for a rapid change of 

 species, and thus enable us considerably to reduce the duration of geologic 

 periods, which had heretofore been measured by data derived from the peiiod of 

 organic stability since the last glacial epoch. 



On the Organization of the Stems of Calamites. 

 By Professor AV. C. Williamson, F.R.S. 



The author pointed out the unity of tj-pe observed amongst the British Calamites, 

 and the consequent improbability of the existence anywhere of two types (the one 

 Cryptogamic, the other Gymnospermous), as believed by Prof. Adolphe Brongniart. 

 He then described the various portions of the jointed stem, the centre of which is 

 a cellular ring of fistular pith, having transverse dissepiments at the nodes. Around 

 this is a woody zone, composed of wedges of barred and reticulated vessels. These 

 wedges are separated from each other by large meduUary rays, and smaller rays 

 separate the constituent laminse of each wedge, which latter spring at their inner- 

 most angle from a longitudinal canal rxmning from node to node. The organi- 

 zation of _ these wedges, canals, and medullary rays was described in mmute 

 detail, their variations in several species being noted, as well as the diiFerences 

 between the arrangement at the nodes and at the internodes, which differences are 

 often very characteristic. The structure of the epidermal layer, or bark, was then 

 shown to be cellular ; it consisted of an iiTegular parenchyma, with cells of variable 

 dimensions. Its exterior appears to have been smooth, unlike the exterior of the 

 woody groove zone, which, like the interior of the latter portion, was longitudinally 

 fluted, the longitudinal ridges and furrows of each internode usually alternating at 

 the nodes. The branches were shown to be of small size, being given off from the 

 woody wedges exactly opposite the centre of each node, whilst the roots were 

 described as originating from the lower extremity of each of the internodes at the 



