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THE POPULAR SCIENCE MONTHLY. 



ly cut but pleasant valley, till it comes to 

 a point where the chalk crosses its course 

 in a semicircular range, and seems as if it 

 would stop its further progress with a dam 

 nearly four hundred feet high. The river 

 has, however, conquered this wall by boring 

 under it a tunnel fifty feet high and half as 

 wide, through which it rushes in a very live- 

 ly torrent. In the course of a little over a 

 hundred yards, it passes a chimney-shaped 

 shaft, which extends to the whole height of 

 the mountain end presents an opening more 

 than thirty feet in diameter at the surface. 

 After another hundred yards the stream 

 crosses the floor of a doline (or sink-hole) 

 four hundred feet broad, and then, after 

 crossing a narrow ledge, enters the great 

 doline of St. Canzian. Here the steep, fre- 

 quently impending rocks on three sides form 

 a gigantic kettle, the western wall of which 

 falls perpendicularly more than five hundred 

 feet. On the southern side a turf-covered 

 slope descends toward the bed of the river, 

 to end abruptly in a precipice of nearly two 

 hundred and fifty feet. Having twice bored 

 the hills for relatively short distances, the 

 Recca continues its course till it meets the 

 rock-wall a third time and excavates a third 

 subterranean channel, this time of thirty- 

 five kilometres, or twenty-two miles. This 

 is the Recca Cave proper, and from it the 

 stream emerges near San Giovanni di Duino 

 into the important river, though a short 

 one, the Timavo, the mystery of the origin 

 of which has been solved by this tracing of 

 the course of its main affluent. 



Scottish and Irish Crannogs. Dr. Rob- 

 ert Munro, in his "Ancient Scottish Lake- 

 Dwellings or Crannogs," draws a parallel 

 between the island-fortifications of the west- 

 ern Celts and the lake-dwellings of Switz- 

 erland, and then suggests a connection of 

 development between the crannog and the 

 moated castle of the middle ages. "Cran- 

 nog " is a Gaelic term, from crann, a mast 

 or tree, and seems to point to the fact that 

 wooden piles or tree-trunks formed an im- 

 portant part in the structure. While the 

 crannogs have several features in common 

 with the Swiss pile-dwellings, they exhibit 

 also some important points of difference, 

 whereas the Irish and Scottish structures 

 are essentially similar. The latter were 



really fortified islands, sometimes natural) 

 but generally artificial. When complete 

 and in use, they would present the appear- 

 ance of small islands surrounded by strong 

 palisades for defense, with buildings of va- 

 rious kinds on their surface, dug-out canoes 

 ready for use, and in some cases a causeway 

 or gangway communicating with the shore. 

 They were certainly built with great skill, 

 and with a solidity of which the endurance 

 of parts of them to the present time is the 

 best evidence. Stone weapons have been 

 found in the crannogs, but the bulk of the 

 remains they yield are of bronze and iron, 

 and some of the coins and pottery point to 

 Roman influences. It is generally admitted 

 that even the Irish crannogs are long sub- 

 sequent in date to the earlier Swiss lake- 

 dwellings. The crannogs, moreover, con- 

 tinued much longer in use than the cor- 

 responding lake-dwellings in Switzerland ; 

 those of Ireland down to the seventeenth 

 century, those of Scotland to a century or 

 two earlier. They were evidently used 

 mainly for defense. In the more northern 

 and wilder parts of Scotland the wooden 

 structures gave way to stone castles, and in 

 the end, as Dr. Munro points out, instead 

 of the castle being brought to the water, 

 the water was brought to the castle in the 

 shape of a moat. It is certainly possible 

 that some individual castles may be the di- 

 rect representatives of former crannogs, but 

 it would be very hard to prove that there 

 has been, as Dr. Munro seems inclined to 

 think, any general connection of the kind 

 between the two structures. 



Effects of Gases on Insects. Mr. L. P. 



Gratacap reports, in the " American Natu- 

 ralist," respecting experiments he has made 

 upon the power of different insects to live 

 in various gases. The Colorado beetle 

 proved the hardiest of them ; it was killed 

 outright in the vapor of prussic acid, which 

 it, however, stood longer than any other in- 

 sect experimented with, while it was para- 

 lyzed for a time in illuminating gas, and died 

 after two hours' imprisonment in nitrous 

 oxide. The effects of oxygen were not very 

 marked ; hydrogen produced lethargy in flies, 

 and was bad for snapping beetles, moths, 

 and a wasp ; carbonic acid killed flies at 

 once, and threw Colorado beetles on their 



