POPULAR MISCELLANY 



859 



the perforations of the teeth by the aborigi- 

 nes of Central America and Yucatan which 

 are mentioned by various authors. Mota Pa- 

 dilla 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 Tejar has the upper front 

 teeth thus bored with cylindrical holes ; and 

 a fragment of an upper jaw dug up at Cam- 

 peachy, 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. 



Iacrease of Temperature in Tunnels. 



Professor G. A. Koch, of Vienna, has been 

 prompted, by the experience of the work- 

 men in the St. Gothard Tunnel, to make re- 

 searches into the phenomenon of increase 

 of temperature which is observed in exca- 

 vating under mountains. Dr. F. M. Stapff, 

 geologist of the St. Gothard Railway, had 

 already published a paper covering the ques- 

 tions of the highest temperature at which 

 it is possible for men to work in subter- 

 ranean 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 coag- 

 ulates (75 G, 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 hori- 

 zontal, 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 Tun- 

 nel 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, in- 

 dicating an increase of about a centigrade 

 degree for every fifty metres. Other obser- 

 vations 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 varia- 

 tions being governed by local influences as 

 well as by the form of the surface. The 

 operation of local influences was very plain- 

 ly observed in the St. Gothard Tunnel, where 

 abundant evidence was gathered that the 

 temperature curves are greatly distorted un- 

 der mountain-peaks. The average rate of 

 increase in the St. Gothard Tunnel, accord- 

 ing to Dr. Stapff, was 1 C. to 48 - 4 metres ; 

 but this rate was considerably exceeded un- 

 der 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 evi- 

 dently conform to the general law of in- 

 crease. Dr. Stapff observed that the tun- 

 nel-water is cooler than the stone when the 

 temperature is less than 24 or 25 ft, but 

 warmer than the stone at above 25 ; and a 

 prediction which he based on this observa- 

 tion, 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 Tun- 

 nel. 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 in- 

 creased 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- 



