the perforations of the teeth by the aborigines of Central America and Yucatan which are mentioned by various authors. Mota Padilla says the Indians cut their teeth down to sharp points and bored holes in them, which they filled with a black cement. A statuette dug up at Téjar has the upper front teeth thus bored with cylindrical holes; and a fragment of an upper jaw dug up at Campeachy, during the French occupation, shows the real teeth marked with precisely similar perforations. The holes appear to have been filled afterward with bluish-green stones. The operation of boring these holes can hardly have been practiced on living persons, and the evidence indicates that it was done after death. No similar mutilations are known to be practiced now anywhere.
Increase of Temperature in Tunnels.—Professor G. A. Koch, of Vienna, has been prompted, by the experience of the workmen in the St. Gothard Tunnel, to make researches into the phenomenon of increase of temperature which is observed in excavating under mountains. Dr. F. M. Stapff, geologist of the St. Gothard Railway, had already published a paper covering the questions of the highest temperature at which it is possible for men to work in subterranean galleries, and the depth under the mountain-mass at which this temperature is reached. Assuming that work begins to be dangerous at the temperature of the blood, 98° Fahr., and that the limits of the vital endurance in animals lie between the temperature at which albumen thickens (60° C, or 140° Fahr.) and that at which it coagulates (75° C, or 167° Fahr.), he deduced that in an extremely dry atmosphere men may keep at work at 50° C. (122° Fahr.), while labor would be impossible at such a temperature in an atmosphere saturated with moisture. The answer to the other question is difficult, because the conditions vary. Descending into the earth from a level surface, the temperature increases at the rate of about 1° C, or 1·8° Fahr., for every thirty-three metres in depth; but the rates fluctuate greatly when the surface is a mountain and the excavation is horizontal, and are governed not only by the height of the overlying mountain above the crown of the tunnel, but also by what is the shortest distance between any point of the tunnel and the nearest point on the surface of the mountain. In the Mont Cenis Tunnel the highest temperature in the stone (29·05° C, or 85° Fahr.) was reached at a depth of 1,607 metres and a distance of 6,448 metres from the southern portal, indicating an increase of about a centigrade degree for every fifty metres. Other observations give rates ranging from 1° C. in twenty-four to 1° in fifty-one metres, and an average of 1° in 37·75 metres, the variations being governed by local influences as well as by the form of the surface. The operation of local influences was very plainly observed in the St. Gothard Tunnel, where abundant evidence was gathered that the temperature curves are greatly distorted under mountain-peaks. The average rate of increase in the St. Gothard Tunnel, according to Dr. Stapff, was 1° C. to 48·4 metres; but this rate was considerably exceeded under the valleys and the plain surfaces, while it was greater than the increase observed under the crests of the mountains. The temperature of the spring-water must evidently conform to the general law of increase. Dr. Stapff observed that the tunnel-water is cooler than the stone when the temperature is less than 24° or 25° C, but warmer than the stone at above 25°; and a prediction which he based on this observation, that springs of a decidedly unpleasant temperature would be met at a certain point in the excavation, was fulfilled to the letter. The fact is an important one, in view of the impossibility of working in a moist and hot atmosphere. The temperature of the air in tunnels is also affected by similar laws, and some very curious facts bearing on this point were noticed in the St. Gothard Tunnel. To the natural increase of temperature in the advance of the excavation must be added the additional heating from the men and animals at work, and from the lights and the explosions, which considerably increased the difficulties in some parts of the excavation. All these things must be taken account of in forming the plans of tunnels and estimating their cost; for the expense of labor must be increased in such places, in proportion as it becomes more difficult and dangerous. If these principles are cor-
