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NATURE 



[February 9, 1922 



tational differentiation during crystallisation as 

 accounting for the production of an underlying 

 gabbro-diorite and an overlying granodiorite from an 

 original basaltic magma ; but granite afterwards in- 

 truded into the more basic of these masses, and has 

 produced a number of "hybrid " rocks. The gabbro- 

 diorite was cold at the time of this intrusion, and. 

 thus lent itself to extensive shattering, and the de- 

 tached blocks have been melted up on an extensive 

 scale. From analogy with undoubted composite pro- 

 ducts, the author considers that the well-known 

 "essexite" of Salem Neck, consisting of the minerals 

 of gabbro side by side with species more rich in 

 sodium, has arisen from similar intermingling and 

 recrystallisation. 



Petroleum Resources of California. — The geo- 

 logy and petroleum resources of North-Western 

 Kern County, California, have been dealt with 

 in a bulletin of the United States Geological Survey 

 (No. 721) recently to hand. New information 

 concerning this interesting region is always welcome, 

 and the oil prospects of this part of the San Joaquin 

 Valley, with its bordering hilly country, would seem 

 to be decidedly favourable. The area described em- 

 braces the already developed fields of Belridge and 

 Lost Hills, which produce oil from Miocene beds, the 

 structures being essentially anticlinal ; prospective 

 areas are suggested in the Temblor Valley (hill region) 

 and in the San Joaquin Valley itself, though in the 

 latter instance "wild-cat" drilling will probably have 

 to be resorted to on account of the thick covering of 

 alluvium masking the solid geology. The detailed 

 work of the California State Mining Bureau on the 

 study of underground structural conditions as affecting 

 development and production of existing fields is now 

 in progress, and as results accrue some further valu- 

 able information should eventuate which may have a 

 far-reaching influence on the progress of development 

 of the untested areas here described. 



Day and Night Distribution of Rainfall.— The 

 differences between summer daytime and night-time 

 precipitation in the United States are the subject 

 of a communication by Mr. W. J. Humphreys in the 

 Monthly Weather Review for June last. A chart 

 based on about 175 Weather Bureau stations is given 

 showing the percentage of average precipitation that 

 occurs at night, 8 p.m. to 8 a.m., for the season April 

 to September over the United States. The various 

 percentages of the twenty-four hours' rainfall that 

 occur at night in different portions of the United States 

 during the summer are shown by curves for each 5 per 

 ■cent, from 25 to 65. Referring to the inequalities 

 between the day and night distribution of summer 

 rainfall, and accepting this as due to the distribution 

 of thunderstorms, it is stated to be consequently in 

 substantially the same proportion as is the strong 

 vertical convection of tolerably humid air. The map 

 shows very markedly that in the south-east portion 

 of the United States the summer rains are most fre- 

 quent during the day, and the author states that 

 most of these rains are due to heat thunderstorms 

 resulting from convection induced by strong surface 

 heating. The excess of rains in the daytime in some 

 other parts of the United States is similarly ex- 

 plained. Consideration is also given to the regions 

 in which the summer rain is most abundant by night, 

 and various causes are put forward. The movement 

 of cool anticyclones is asserted as exercising consider- 

 able influence in the main by "breaking" the "hot 

 waves " of the Mississippi, Missouri, and Ohio vallevs, 

 thunderstorms being developed. In parts the cooler 

 NO. 2728, VOL. 109] 



air is said to overflow the warmer, and thereby estab- 

 lishes that convectional instability essential to the 

 genesis of the thunderstorms. In this way the author 

 is of opinion that in parts at least the thunderstorm 

 is more frequent and the summer precipitation more 

 abundant during the night than during the daytime. 



Gravity Observations. — The United States Coast 

 and Geodetic Survey has issued as a Special 

 Publication (No. 69) a report by Mr. Clarence H. 

 Swick on " Modern Methods for Measuring the 

 Intensity of Gravity." The instruments and 

 methods, which are dealt with in usefully great 

 detail, are those employed by the Survey for 

 their gravity expeditions. The determinations are 

 made with half-second (quarter-metre) pendulums, 

 which in 1890 replaced the metre pendulums formerly 

 used. This step marked an epoch in the gravity work 

 of the Survey ; the change not only greatly reduced 

 the cost of transport and of preparing the stations, 

 but also increased the accuracy so much as to render 

 the observations prior to 1890 obsolete as material for 

 investigations into the theories of gravity and isostasy. 

 The observations made are relative, the time of oscil- 

 lation of the pendulums measured at each station 

 being compared with the corresponding times at the 

 pendulum-room of the Survey in Washington, where 

 the absolute value of gravity has been carefully deter- 

 mined. The pendulums are swung at low pwessure in 

 an airtight case, and corrections are applied for tem- 

 perature, pressure, arc, flexure, etc. An interfero- 

 meter is used to determine the flexure of the pendulum 

 support. Up to 1920 the number of gravity stations 

 "occupied " with the modern instruments was 276, of 

 which 230 were established since 1909. In 1920 a 

 further important instrumental improvement was 

 introduced by the construction of pendulums with invar 

 instead of bronze ; the reduction of the temperature- 

 coefficient to one-fifteenth its former value greatly 

 simplifies the observing conditions. Another advance 

 is the use of wireless signals for determining the 

 chronometer rates. The report closes with an interest- 

 ing appendix instructing the observer in the art of 

 justifying his work to the lay citizen of the United 

 States, by explaining briefly the purpose and value of 

 gravity observations. 



Tests of Weldless Steel Tubing. — A paper 

 by Mr. W. W. Hackett read before the Institution 

 of Automobile Engineers gives an account of a 

 large number of alternating stress experiments on 

 weldless steel tubing such as is used in motor- 

 cycles and on components, e.g. motor-cycle forks. 

 These experiments enable the author to make several 

 suggestions for improvements in constructional details. 

 He also makes out a case for the use of tubes made 

 from steel containing a higher percentage of carbon 

 than has formerly been accepted. From experiments 

 carried out during the war period on aeroplane tubing 

 it was found that excellent results could be obtained 

 by using 0-5 per cent, carbon steel tubing, giving in 

 the bright or blued state a yield of 40 to 45 tons per 

 sq. in. and an ultimate stress of 45 to 50 tons per 

 sq. in. ; when annealed, the steel should give 23 tons 

 {>er sq. in. yield and 35 tons per sq. in. ultimate. The 

 author has found that in the motor trade there was 

 no inclination to use these high-carbon steel , tubes, 

 for it was feared that they would be brittle. The 

 author's tests were carried out on joints brazed in 

 his shops in a commercial manner, and show con- 

 sistently that the 0-5 per cent, carbon steel has always 

 been superior to 03 per cent, steel, and that the latter 

 has always been better than o 15 per cent, steel. 



