January ii, 1889.] 



SCIENCE. 



19 



pipes and in drops to the eccentric, but valves are provided on the 

 pipes so that the supply can be regulated as desired ; and the res- 

 ervoir can be supplied with fresh oil while the engine is running. 

 Besides the saving in oil, these devices keep a clean and presentable 

 engine and engine-room. 



The automatic cut-off governor is shown in Fig. 3. It is an 

 isochronous governor, very simple in construction, and responds 

 instantaneously to the slightest variation in load, cutting off the 

 steam at a point that will just do the work and maintain the fi.xed 

 speed of the engine. It is secured to the side of the fly-wheel, and 

 connects direct through the eccentric on the main shaft with the 

 valve, without the use of gearing, pulleys, shafts, or belts. All its 

 parts are in sight, and are readily accessible for cleaning. It gives 

 an open port at the beginning of each stroke, admitting steam to 

 the piston at full boiler pressure, and varies the point of cut-off as 

 the load requires, from the beginning to three-fourths of each 

 stroke. The speed of the engine remains practically constant, re- 

 gardless of the change of load or variation of steam-pressure 

 in the boiler, the variation from no load to the full power of 

 the engine being, it is claimed, less than one per cent. The 



SCIENTIFIC NEWS IN WASHINGTON. 



Does Exposure to the Sun cause the Human Skull to be Harder and 

 Thicker? — Diseases of Menagerie Animals. — The Geological 

 Survey. 



Does Exposure to the Sun cause the Human Skull to be 

 Harder and Thicker ? 



One of the most interesting things mentioned by Professor Vir- 

 chow in his little book just published, entitled " Medical Remem- 

 brances of an Egyptian Journey," in which he describes an e.xcur- 

 sion up the Nile as far as the first cataract, is that the broken 

 skulls on the first great sepulchral fields, dating from Roman times, 

 are as thick and hard as Herodotus says those of the slain Egyp- 

 tians were in comparison with the brittle ones of the Persians. 

 The Greek historian explains this by attributing it to the early ex- 

 posure of children to the heat of the sun ; and in many parts of 

 upper Egypt the German travellers actually found young children 

 thus exposed during their parents' absence in the fields, in im- 

 mense clay bowls, resembling in shape a champagne-glass with a 

 stem, into which they were put without shelter. 



dash-pot attached to the eccentric prevents any sudden move- 

 ment of the weight when a great change of load occurs suddenly. 

 The running speed of the engine may be changed to suit require- 

 ments by shifting the position of the weight on the lever. 



The steam-chest is bored out and fitted with a pair of cylinders 

 or bushings which have supporting bars across the ports, to pre- 

 vent any possibility of the valve catching upon the ports. The 

 valve is of the hollow piston type, — a hollow tube, with a piston 

 at each end. It is surrounded by steam, which presses equally 

 upon each end. thus perfecily balancing the valve and relieving its 

 pressure, insuring it long service with little wear. The piston-head 

 is a single casting, hollow, and as light as is consistent with 

 strength. The cross-head is a crucible steel casting, with phos- 

 phor-bronze slides ; and the attachment to the connecting-rod is 

 central, thus avoiding any strain on the piston-rod by angular 

 thrust. The guides are bored out the same size as the cylinder, 

 thus insuring large wearing surfaces and constant accuracy of line 

 with cylinder. This, together with the self-oiling devices, insures 

 cool running, and long service without adjustment. It may be 

 added, that the construction seems to be such as to give the re- 

 quired strength and rigidity for high speeds ; ample wearing sur- 

 faces are provided ; all the parts are made of steel, phosphor- 

 bronze, and charcoal iron, and are interchangeable ; and every 

 engine is tested by actual service at the factory. 



This discovery by Professor Virchow is interesting, because it at 

 once suggests the question whether the proverbial thickness of the 

 skull of the negro has not been caused by exposure to the sun, and 

 whether it is a peculiarity of savages of tropical countries that their 

 skulls are thicker and harder than those of the inhabitants of tem- 

 perate and colder countries. 



Students of craniology have never made any investigation to as- 

 certain whether the skulls of different races vary in degrees of 

 hardness. It would be almost impossible to make such an inquiry. 

 As is well known, the human skull increases in hardness from 

 childhood to maturity and age. A miscellaneous collection of 

 skulls of any given people would therefore be of no value in such an 

 investigation. To obtain a collection of skulls of a number of na- 

 tionalities, that should be taken from subjects all of the same age, 

 to have them all similarly prepared and in sufficient numbers to 

 make it possible to draw any general conclusions from their com- 

 parison with each other, would be manifestly impossible. 



More attention has been given to the relative thickness of differ- 

 ent skulls, or rather to their weight, from which their thickness 

 may be inferred. Of the large collection of crania in the Army 

 Medical Museum at Washington, the thickest are those of negroes 

 and Alaskan Indians. The skulls of other Indians, both of North 

 and South America, in tropical or temperate cHmes, and of the 

 Eskimo, do not appear to be particularly thick. Among the ancient 



