•260 



SCIENCE. 



|Voi.. II., No. ro. 



stances, tliey arc extremely liable to lueak in 

 liandling. Jf the snow has been properly tested, 



lliis slioulfl, however, seldom occur. The trench 

 completed, and enough blocks secured to form 

 the first or base course, the floor 

 is laid out by a circular sweep of 

 tlie knife, varying in diameter, of 

 course, according to the number 

 of intended occupants. Com- 

 mencing at tlie left hand, this 

 course is laid until the first block, 

 a, is i-eached, wliich is cut in 

 halves from its first lower corner, 

 c, along the ascending diagonal ; 

 and the top half, /),, is tin-own 

 away. The last block, b, has its 

 c-pnliguous corner cut off; so that 

 the next block, shown in broken 

 outline, ascends and forms the 

 first bloci< of the next course. 

 The igloo is then formed of this 

 spiral of snow-blocks, each course 

 inclining inward slightly more 

 than the one i)revious, until the 

 last, wliioh may be called the 

 key-block, is pei'fectly horizontal, 

 and firmly wedges in and binds 

 the whole struciure. This spiral 

 form of the courses I have tried 

 to show in the illustration of one 

 of the half-completed igloos. 



1 know that the general idea is, that each 

 coui'se is complete within ilself, like a course 



Ihis to be almost impossible, as Ihc first lilock 

 in the course, alter tlicy had connnenccd to 

 lean considerably, would have to be supported 

 until it was flanked by others ; and these, again, 

 would be very unstable. In fact, one often 

 wonders how a snow-block will hold in place 

 against its own weight, leaning far inwards, 

 almost horizontal, and suppoited only on two 

 sides, and will imagine that the native woi'k- 

 manship must be very good to give such re- 

 sults. As the blocks approach the top, — where 

 the}- are more nearly horizontal and more lia- 

 ble to tumble down, — their figure becomes 

 trapezoidal in order to keep the vertical joints 

 pointing to the centre and top ; and, while sup- 

 ported on but two sides, these form a more or 

 less acute angle, — more acute as it is needed 

 and approaches the top, where the last few 

 blocks are made triangular and meet at a point. 

 The workman stands inside until it is com- 

 pleted. Despite all the care, the falling of 



THE HALF BUILT IGLOO 



: 



of 1 ricks on a round tower in our method of 

 liui ding ; but a moment's thought would show 



t)locks is a very common occurrence, and ha])- 

 l)ens with nearly ever}' building. 



It will be remembered that the base course 

 has been laid upon a sloping bank of snow, the 

 lowest point being at the door, which has been 

 formed by the trench running into the build- 

 ing. Therefore, when the builder is coming- 

 down with a course of blocks on the left side, 

 they are peculiarly prone to tumble in. The 

 fact that this siide is used for starting up on the 



