534 



NA TURE 



[October 28, 1909 



expressed in British thermal units radiated per square foot 

 per hour as i6x io-'°(T,'' — T,''), where 'i\ and T^ are 

 the temperatures of the incandescent gases and of the 

 boundary respectively in degrees Fahrenheit absolute. 

 This formula may be applied in order to find a theoretical 

 upper limit to the quantity of heat radiated to the fire- 

 box boundary on the assumption that the flame is actually 

 composed of solid masses of incandescent carbon, and so 

 follows Stefan's law. Thus, with flame and Ijoundary 

 temperatures respectively of 3000° and 800° F. absolute, 

 the heat radiation is 129,600 British thermal units per 

 square foot per hour. With temperatures respectively of 

 4000° and Soo° the radiation amounts to 410,000 British 

 thermal units, showing the rapiditv of increase of radia- 

 tion as the flame temperature rises. Stefan's law does 

 not apply to cases where the gases are not incandescent. 



In transmission by conduction and convection the heat- 

 How path from the interior of the mass of gas in the fire- 

 box to a point in the interior of the mass of water is 

 made up of the following parts : — the gaseous part from 

 the starting point to the gas film clinging to the plate ; 

 the gas film itself ; the surface of contact between the 

 plate and the gas ; the metallic plate ; the surface of con- 

 tact between the plate and the water ; the water film ; 

 the water from the film to the point in the mass of water. 

 To these must be added, for dirty plates, a layer of sooty 

 deposit on the gas side and a layer of scale on the water 

 side, on which there may also be a deposit of oily matter. 

 There is evidence that qS per cent, of the total " tempera- 

 ture " head. is required in order to force the heat from 

 the gas into the plate, the remaining 2 per cent, alone 

 being required to transfer the heat from the plate to the 

 water in the boiler. The presence of oily matter mav 

 raise the temperature difference between the hot side of 

 the plate and the water from 68° F. to 550° F., depend- 

 ing on the nature and thickness of the greasv deposit. 

 The thickness of the film of gas clinging to the plate is 

 probably of the order of i /40-inch, and accounts for the 

 greater part of the resistance offered to heat transmission 

 by the total path of flow. The water film clinging to 

 the plate also contributes to the resistancCi as convection 

 currents cannot exist in it, and heat must be transferred 

 across it by the conductivity of the water forming the 

 film, which is known to be exceedingly small. 



If these films be completely or partially destroyed, the 

 head required to effect the heat transmission from the 

 gas to the water across the plate will be considerably 

 reduced. One of the most potent factors in disturbing 

 the gas film is the velocity possessed by the moving gases". 

 Most of the work in connection with heat transmission 

 since the time of Rankine shows attempts to introduce a 

 velocity factor variable into the expressions. Again, 

 owing to the temperature gradient from the centre of the 

 flue gases to the boundary, the efficiency must increase 

 with a decrease in the size of the flue within limits. Hence 

 the hydraulic mean depth of the flue must form a factor. 

 The importance of good water circulation lies in the fact 

 that forcing water across the heating surface with a high 

 velocity has the effect of breaking up the water film. 



Notwithstanding the large number of researches bearing 

 on the subject of heat transmission, there is a general 

 absence of complete data regarding the actual phenomena 

 occurring in a steam boiler when working under ordinary 

 conditions of practice. For instance, no data exist which 

 gives the temperature gradients at different parts of n 

 boiler flue with accuracy. Researches have had little effect 

 in modifying the general design of steam boilers, although 

 the costly nature of these may be understood from a set 

 recently made by the United States Geological Survey, 

 costing 100,000 dollars. The author suggests that the 

 institution might undertake a research in which steam 

 boilers of different types under practical conditions m.nv 

 have all the elements of their working measured, together 

 with temperature measurements for the purpose of 

 establishing the temperature gradients at different parts 

 of the heating surface. Such a research would be costly, 

 but would be well worthy of the institution. 



The paper contains elaborate indexes giving reference 

 to all known work bearing on the subject ; these will be 

 extremely valuable to all interested in heat transmission. 

 NO. 2087, VOL. 81] 



THE ANTIQUITY OF MAN IN SOUTH 

 AMERICA. 



'F'HE view^s held by Dr. Florentino Ameghino as to the 

 antiquity of man in South .\merica are based on 

 the occurrence of split bones, and bones showing signs of 

 haying been cut, side by side with certain scoriaceous pro- 

 ducts, the '■ tierras cocidas " of .'\rgentina. We are not 

 as yet in possession of figures of the bones, and it may 

 be presumed that they are regarded as of less importance 

 than the baked and reddened earths. A lively controversy 

 has arisen round the latter, and the question appears tcv 

 be one that must be decided by the geologist rather than 

 by the anthropologist. 



Several series of deposits of Cainozoic age are recog- 

 nised along the curving coast-line south of the mouth of 

 the Rio de la Plata, past Mar del Plata, and away 

 towards Bahia Blanca. The orientation of one of Dr. 

 .Ameghino's maps is unsatisfactory ; but much topo- 

 graphical and descriptive matter will be found in his paper 

 on " Las formaciones scdimentarias de la regi6n litoral 

 de Mar del Plata y Chapalmaldn " (Anales del Museo 

 nacioiial de Buenos Aires, tomo xvii., p. 343 ; published 

 November 28, 1908). This, so far as the baked earths are 

 roncernod, is overshadowed by a memoir by Senor Outes, 

 Dr. Ducloux, and Dr. H. Biicking, of Strassburg, issued 

 on September 15 of the same year (" Estudio de las 

 supuestas escorias y tierras cocidas de la serie pampeana 

 de la Republica Argentina," Revista del Museo de la 

 Plata, tomo xy., p. 138). 



The two authors who have called in Dr. Biicking to 

 their assistance review the question historically. The 

 Araucanian formation, with the Monte Hermoso beds, 

 which Florentino .Ameghino prefers to regard as Miocene, 

 is very generally placed by other authors in the Pliocene ; 

 but this does not affect the arguments of Outes and 

 Ducloux. They point out that in 1865 Heusser and 

 Claraz, in a paper published in French at Ziirich, recog- 

 nised cellular, and apparently volcanic, material in the 

 lower part of the Pampas beds near Mar del Plata. 

 More than twenty years later, in 1887, Florentino 

 .Ameghino gathered similar " escorias " at Monte Hermoso, 

 60 km. north-east of Bahia Blanca, and in 1889 described 

 others from the neighbourhood of La Plata. These places 

 are, of course, all remote from any volcanic vents that 

 have so far been discovered. 



Meanwhile, from 1874 onwards, the more obscure 

 materials known as " tierras cocidas " were collected by 

 Senores Juan, Carlos, and Florentino Ameghino from 

 various places in the province of Buenos Aires, and the 

 last-named writer claimed them as traces of ancient 

 hearths, and as indicating man's antiquity in South 

 .America. The field \vas \videned by other observers, and 

 the typical specimens, with new ones personally collected, 

 have now been investigated by Outes and Ducloux. 



These authors make no claim to originality in rejecting 

 the opinion of Florentino Ameghino. They quote the 

 views of Steinmann in 1906 (p. 160 of their memoir) as 

 to the andesitic nature of the scori.-e and baked earths, 

 and they go back (p. 191) to Charles Darwin, who re- 

 corded, in 1851, the occurrence of pebbles of pumice on 

 the surface of the raised terrace at Monte Hermoso. 

 Darwin attributed these pebbles to the transporting action 

 of ancient rivers, and pointed out how^ the rivers Negro 

 and Chupat bring down volcanic pumice and scoriae at 

 the present day. Outes shows that such materials need 

 not have been carried directly from the .Andes, but may 

 have been washed out of the detrital volcanic beds of the 

 Araucanian formation, which is much older than the 

 Pampas beds, and possibly than those of Monte Hermoso. 

 The inclusion of vegetable remains in the scorife is held 

 not to militate against their volcanic origin. Doering has 

 urged the importance of laterisation in determining the 

 characters of the red beds in the Lower Pampas series, 

 and Outes (o. iq4l Quotes his views with approval as 

 explaining many of the "baked earths." The elaborate 

 chemical work of Ducloux (op. 162-184) goes to show 

 that the loess of th^ Pampas beds and the included scoris' 

 and " baked earths " have a similar chemical composition, 

 and masses like volcanic scoria; have been made artificially 



