SCIENCE. 



395 



laid upon the importance of carefully marlcing sta- 

 tions; and the detailed instructions in regard to the 

 subject occupy two quarto pages in the manual ' On 

 the field-worlc of triangulation,' issued by the survey. 

 The most common method used is the one which 

 has been copied by the N. T. state survey. Other 

 methods, however, are used in special cases. For 

 recovering a station, tlie main dependence is upon 

 the surface-marks, and the underground-marks are 

 used only for protection in case of the destruction of 

 the others by accident or design. 



H. W. Blair, 

 Assistant Coast and geodetic survey. 



Washington, D.C., 

 April 22, 18S3. 



Freezing of liquids in living vegetable tissue. 



The conclusions of Mr. Meehan in relation to tlie 

 above topic (Science, p. 229) seem to me scarcely 

 warranted by the best authenticated facts in vegeta- 

 ble pliysiology. Experimental investigations and re- 

 searches, undertaken many years ago, led me to the 

 following deductions : ^ — 



1. That the sap of many living plants can be frozen 

 by the application of a degree of cold not much below 

 that required to freeze it when removed from the 

 plant; and that in very cold climates the sap of all 

 perennial plants must he frozen in all parts during 

 the winter months. 



2. That the congelation of the juices of living vege- 

 tables does not, as many phytologists have imagined, 

 necessariljf and inevitably result in the deatli of the 

 whole plant, or of the part in which it takes place, 

 but, on the contrary, that frequently no injurious 

 consequences follow. Consequently it is unwarranta- 

 ble to assume that a plant which is not Icilled by 

 severe cold never was frozen ; and therefore it is un- 

 necessary to invoke tlie aid of a ' vital power ' to 

 enable plants to survive the influence of cold suf- 

 ficiently intense to freeze their juices when removed 

 from tlie living plant. 



3. That the burstiug of the trunks of trees in high 

 latitudes is not due to the expansion which the sap 

 undergoes in process of congelation, but to the un- 

 equal contraction which takes place in the trunk 

 (usually after the complete congelation of its juices) 

 in consequence of a sudden depression of tempera- 

 ture. In short, tliat the rupture of the trunk in such 

 cases is due to the same cause as the rents in the frozen 

 ground, and tlie cracks in large slieets of thick ice, 

 which occur in liigli latitudes when there is sudden 

 accession of cold. This view is fortified by the fact 

 that the coefficient of contraction (or expansion) of 

 ice is greater than that of any 'other solid body hith- 

 erto examined, with the exception of hardened caout- 

 chouc, or ebonite. John LeConte. 



Berljeley, Cal., April 1", 1833. 



Sun's radiation and geological climate. 



In his review of Whitney's climatic clianges, Mr. 

 Gilbert says, "His [Whitney's] hypothesis that tlie 

 intensity of solar radiation is gradually lessening, by 

 reason of the dissipation of solar energy, . . . will be 

 admitted by most students." Mr. Whitney and his 

 reviewer fall into tlie very natural error, that a loss 

 of heat, and, of course, of energy, is necessarily ac- 

 companied by a fall in temperature. Paradoxical as 

 it may appear, a loss of both heat and energy may 



1 For the exposition of the basis of these deductions, the reader 

 is referred to the memoir of the writer, entitled " Observations 

 on the freezing of vegetables, and on the causes which enable 

 some plants to endure the action of extreme cold." — (Proc. 

 Amer. asffoc. adv. -sc, vi. 338-359; Amer. joum. hc. [2], xiii. 84- 

 92, 196-206.) 



produce a rise in the temperature of the body that 

 losesthem. If it be true that the sun is, as is now 

 thought by many eminent scientists, a globe of gas- 

 eous matter, then, under the long process of giving 

 off heat, it has actually been growing hotter, and the 

 intensity of its heat on the earth's surface to-day is 

 greater than it was in the early geological epochs. 



The world is indebted for this curious fact to 

 Mr. J. Homer Lane.' I quote from Newcomb's As- 

 tronomy, p. 508: "The principle in question may be 

 readily shown in tlie following way: if a globular, 

 gaseous mass is condensed to one-half its primitive 

 diameter, the centra) attraction upon any part of its 

 mass will be increased fourfold, while the surface 

 upon which this attraction is exercised will be re- 

 duced to one-fourth. Hence the pressure per unit 

 of surface will be increased sixteen times, while the 

 density will be increased only eight times. Hence, 

 if the" elastic and gravitating forces were in equi- 

 librium in the primitive condition of the mass, Its 

 temperature must be doubled in order that they may 

 still be in equilibrium after the diameter is reduced 

 one-half." 



Admitting, then, the gaseous condition of the sun, 

 as, under our present knowledge, we seem compelled 

 to do, we must also admit that the intensity of the 

 sun's radiation of heat has been slowly increasing 

 through tlie ages, and to-day is greater than at any 

 previous time. 'The increase may have been small; 

 but, so far as there has been any change, it has been 

 in the direction of an increase, and hence cannot 

 explain the undoubted decrease in the general tem- 

 perature of the earth's atmosphere indicated by the 

 paleontological record. C. B. Wakring. 



Distribution of public documents. 



Few outside of the ranks of professional politi- 

 cians will disagree with the report of the committee 

 of Congress on the printing and distribution of pub- 

 lic documents, or with the tenor of the editorial re- 

 marks on the subject in No. 9 of Science. But it is 

 to be feared that it will be as difficult to induce the 

 average congressman to dispense with these lubri- 

 cants of the political machine as with the senseless 

 distribution, through the department of agriculture, 

 of seeds that can as well be bought at any country 

 store. If any means can be devised by which the 

 'costly and beautifully illustrated volumes' shall 

 reach those for whose information they were written, 

 instead of serving to adorn the nurseries of influen- 

 tial ward strikers and campaign committee men, it 

 will redound greatly to the benefit of scientific knowl- 

 edge and progress ; for at present it is mainly through 

 the medium of second-hand book-stands that those 

 interested can occasionally get tlie professional works 

 of which their political insignificance did not render 

 them worthy recipients. 



There is one notable exception, liowever, to this 

 extravagance and misdirection of precious docu- 

 ments, the result of one of those spasms of virtue 

 mentioned in the editorial. I refer to the law con- 

 cerning the distribution of the publications of the 

 geological survey, to which director Powell has called 

 attention in a circular issued some time ago. Accord- 

 ing to the terms of this law, these documents, except- 

 ing the general report, can be obtained only by pur- 

 chase or exchange ; that is, the scientific workers of 

 the country may at first get what may be deemed the 

 equivalent of their own publications, or, possibly, of 

 rare works in their possession. But wlien this re- 

 source is exhausted, the only method open to them, 

 for obtaining what in many cases is the sequel of 

 1 See Amer. jimrn. sc, July, 1870. 



