526 



NATURE 



{Oct. 2, 1879 



the earth, a tabic (p. 100) of the mean monthly tempera- 

 tures of Greenwich from October, 1846, to December, 

 1873, is given. The method by which this table was 

 constructed is thus described :— 



"The values for 1847 are the simple means of two- 

 hourly observations; those for 1848 are the means of 

 usually six observations daily, corrected for diurnal 

 inequality by application of corrections derived from Mr. 

 Glaisher's paper ' On the Corrections to be Applied to 

 Meteorological Observations,' in the Philosophical Trans- 

 actions for 1848, Part i. The means for 1849 and all 

 succeeding years are found by combining eye-observa- 

 tions, taken usually four times on each day, and corrected 

 for diurnal inequality, with observations of the maximum 

 and minimum corrected by a quantity (taken from Mr. 

 Glaisher's paper) peculiar to the period of the year. These 

 temperatures may be regarded as accurate mean tempe- 

 ratures." 



From this table the annual mean temperature of Green- 

 wich comes out as 49''43, being I'-g, i°7, 2°'i, i°'4, and 

 i""l in excess of the earth thermometers from the surface 

 downwards. This large excess raises a doubt as to the 

 correctness of the method adopted in calculating the mean 

 temperature at Greenwich. Looking at Table 43 we find 

 the mean temperature at every hour of the day for the 

 month of June, with the number of days each, of the 

 years for which obser\'ations were available for striking 

 the means. On eight of the years the record was com- 

 plete, and on these years, therefore, the mean tempera- 

 tures deduced by the two methods should agree closely, if 

 the method of calculating the means quoted above be a 

 correct one. A comparison shows that in none of the 

 months is there any agreement, the extreme differences 

 being i°'S for June, 1865, and o°7 in June, 1863, and the 

 mean difference for the whole eight years, i"'o. The true 

 mean — that of the twenty-four observations each day — is 

 in all these cases in excess of the other mean. Similarly 

 May, October, and January were examined, with resulting 

 mean differences of o°-s, o°-3, and o°-2 respectively. It 

 follows that the mean temperatures, which are the most 

 important element in the climate of Greenwich, remain 

 still to be calculated. 



When this has been done it will probably be found that 

 the mean annual temperature of Greenwich has been 

 understated by half a degree, and that consequently the 

 mean for the twenty-eight years ending with 1873 was 

 yp'o. This supposition is rendered the more probable 

 by applying the noon correction from Greenwich daily 

 inequality tables to the mean of the temperature inside 

 the perforated box protecting the earth thermometer. The 

 mean annual temperature then becomes 50°'!. 



In a large number of the years the third barometric 

 maximum, first noticed by Rikatscheff as occurring in 

 certain regions of the globe a little after midnight, appears 

 in the Greenwich diurnal curves for December, January, 

 and February, less frequently in March, and seldom or 

 not at all in the other months. The somewhat rough 

 method which has been adopted in reducing the baro- 

 metric observations to 32° unfortunately renders the 

 evidence furnished by the Greenwich results regarding the 

 more refined inquiries of meteorology, such as this, and the 

 mean diurnal inequality of the barometer in the lunar 

 months, not so satisfactory and conclusive as might have 

 been wished. Alexander Buchan 



CHEMICAL DENUDA TION AND GEOLOGICAL 

 TIME 



Chemical Denudation in Relation to Geological Time. 

 By T. Mellard Reade, C.E., F.G.S., Past President of 

 the Liverpool Geological .Society. (London: David 

 Bogue, 1879; PP- 6i)- 



THIS little book is made up of three papers : one on 

 " Geological Time ; " a second on " The Geological 

 Significance of the Challenger Discoveries ; " and the 

 third on " Limestone as an Index of Geological Time.'' 

 The last paper was read before the Royal Society in 

 January, 1879, ^'^^ 'he others have been read before the 

 Liverpool Society, of which the author is a distinguished 

 member. Although, therefore, not new, these papers are 

 well worth reading, for a vast amount of good solid fact 

 is environed by curious calculations, and by hypotheses 

 of a highly exciting nature. That is to say, exciting to 

 the prosy realistic disposition of modern geology. This 

 meritorious work, however, is slightly depreciated by the 

 introduction of matter which is not strictly consistent 

 with the results of modem research. Nevertheless, on 

 the whole, the work may be considered very satisfactory 

 by those who believe that doubt is the mother of progress ; 

 for all the hypotheses and conclusions in it are the 

 product of a geological imagination of the highest and 

 most vigorous order, and are of course open to objection. 

 In the introduction it is stated that the author, during an 

 attempt to estimate the amount of " solid matter conveyed 

 annually in solution " in river-water to the sea from the 

 surface of England and Wales, had a "new modulus" 

 come into his mind, which might enable him to gauge the 

 vista of the immensity of past time, or rather to arrive at 

 "a minimum limit to the age of the earth." The result is 

 thus stated: "If we imagine the area of England ard 

 Wales consisting of 58,300 square miles, to form one 

 river-basin, the delivery of water by such river would be 

 68,450,936,960 tons, or 1 8 '3 inches per annum, containirg 

 a total of 8,370,630 tons of solids in solution, representir g 

 a general lowering of the surface from that cause alone of 

 •0077 of a foot per century, or one foot in 12,978 years." 

 Taking the "soluble denudation" of other parts of the 

 world into consideration, Mr. Reade considers "that about 

 100 tons of rocky matter is dissolved by rain per English 

 square mile per annum." This he states contains 50 

 tons of carbonate of lime, and twenty of sulphate of lime, 

 &c., and proceeds : " If, as is generally supposed, the sea 

 contains only what is washed into it from the land, and 

 we can estimate its numeral contents in tons, we at once 

 get a minimum measure of the age of the earth." As 

 Herschel states that the ocean contains 2,494,500 billions 

 of tons of water, and the mean of Dr. Frankland's analysis 

 gives 48 '9 tons of carbonate of lime and magnesia, and 

 1,017 tons of sulphate of lime and magnesia in 100,000 tons, 

 it follows, according to the author, that it would take 

 25,000,000 of years to accumulate the quantity of sulphate 

 of lime and magnesia contained in sea water, but only 

 480,000 years to renew the carbonate of lime and magnesia, 

 and the discrepancy is caused by the appropriation of the 

 calcic carbonate by mollusca for their tests. The amount 

 of visible sediment brought down mechanically by rivers, 

 as calculated for the whole world upon the results of 

 Humphreys and Abbot for the Mississippi, and the 



