August 19, 1922] 



NA TURE 



253 



reduced to standard conditions is maintained constant 

 to within yL- per cent. The corrections effected over 

 a period of a month are automatically recorded on a 

 drum revolving above the device. The method of 

 mounting the meter drum loose on a screwed axle 

 also prevents the occurrence of accidents should the 

 gas supply be temporarily cut off and resumed later, 

 or should the water flow cease. The possible inter- 

 ference of a mouse with the righting of the bucket 

 after emptying is also ingeniously provided for. 



The Calorimeter Proper. — This is shown in 

 vertical section in Fig. 4. A and B are the hot 

 and cold water chambers respectively ; C is the 

 heat interchanger, in which the heat of the 

 products of combustion derived from gas 

 burning at the fused - silica burner, D, is 

 communicated to the stream of water. A 

 silica dome is disposed above the flame. The 

 interchanger is made of sheet-lead closely 

 folded into fifteen zig-zags round the central 

 combustion space. Narrow up-cast water-ways 

 are then formed on one side of the sheet, and 

 down-cast gas-ways on the other side. The 

 heated water passes to B through the narrow 

 neck in the double partition, E, a device in- 

 troduced by Prof. Boys to prevent the 

 calorimeter indicating more heat than is pro- 

 duced by the gas. The copper cylinder, F, 

 fixed to the brass ring, G, is so proportioned, 

 that loss of heat from the upper part of 

 the hot-water compartment is compensated 

 by the equal gain from the cylinder lower 

 down by the heat interchanger. 



The operative thermometers, H and J, are of brass, 

 and are filled with amy] alcohol. They are closed 

 with corrugated brass covers. A lever system utilising 

 the third dimension of space, magnifies the deformation 

 of the respective covers occurring with change of 

 temperature, and the net difference of temperature 

 of the two thermometers, due to heating, controls 

 the position of an inked pen recording on a roll of 

 paper, seen on the right of Fig. 1, kept in motion by 



the clock. On the paper parallel lines are ruled 

 during the rotation, indicating definite percentage- 

 departures of the actual measured calorific value of 

 the gas from the declared calorific value. Time 

 indications are in like manner impressed upon the 

 record. An integrating device shown on the right of 

 Fig. 4, operating after the manner of the Amsler 

 planimeter and controlled by the position of the 

 recording pen, averages the departures of the calorific 

 value of the gas from the declared calorific value since 



the indicator was last set to zero, i.e., since the begin- 

 ning of the quarter, so that, for example, the integrator 

 indicating + 5 would signify a 5-day 1 per cent, excess 

 of calorific value, or a i-day 5 per cent, excess, etc. 

 The writer is extremely obliged to Prof. Boys for the 

 kind manner in which he has afforded information 

 concerning the instrument, and to Messrs. Griffin and 

 Sons for providing the illustrations reproduced in this 

 article. 



The Earth's "Crust" and its Composition. 



By Thomas Crook. 



THE term " crust " is frequently used in dealing 

 with the constitution of the earth, but is seldom 

 defined. It is a convenient scientific term to apply 

 to the earth's outermost shell, the only portion of 

 which geologists have much positive knowledge, and 

 if it is put to scientific use, it should be defined, 

 although a definition of it may involve some hypo- 

 thesis as to the physical condition of the earth's 

 interior. 



According to Arrhenius, who assumes that the tem- 

 perature-gradient observed in continental areas is per- 

 sistent in depth, the temperature of the earth's interior 

 greatly exceeds that of the critical temperature of the 

 materials occurring there. He infers therefore that 

 the interior is for the most part gaseous though rigid, 

 and that this gaseous core is separated by a molten 

 layer from an outer solid shell about 40 miles thick. 



NO. 2755, VOL. I io] 



Osmond Fisher assumed a molten condition at a depth 

 of 25 miles. To those who accept this view, the term 

 " crust " has a very real and simple significance : it is 

 the thin, solid, outer shell of the earth, underlain by 

 molten magma. 



At the present time, however, this hypothesis appears 

 not to be widely held among geophysicists, most of 

 whom follow^ Lord Kelvin, Sir George Darwin, and 

 other eminent authorities who have shown good reasons 

 for rejecting the hypothesis of a molten interior at 

 such depths as postulated by Fisher and Arrhenius, 

 and who claim that the earth is solid throughout. For 

 those who adopt this view the definition of the earth's 

 " crust " is a more difficult matter. 



The prevalent view at the present day as regards 

 the constitution of the earth's interior is that it consists 

 of an inner core of nickel-iron about 6200 miles in 



