534 THE POPULAR SCIENCE MONTHLY. 



nearly the actual frequency of occurrence agreed with the theo- 

 retical average frequency. 



We might mention, also, a number of parlor-games which in- 

 volve some degree of muscular exercise ; and others, like the game 

 of twenty questions, which require vivacity and brightness in the 

 use of language. But the main principles to which we wished to 

 call attention have been sufficiently illustrated by the sedentary 

 games and solitaires which we have already mentioned. The 

 therapeutic value of a game depends upon its adaptation to the 

 individual tastes and needs of the person who takes it up. It 

 must be such as to interest him and keep his attention, and yet 

 not such as to absorb, excite, and fatigue him. His native and 

 acquired tastes, his age and habits of life, the state of his health, 

 the causes of his fatigue, or of his illness — all these, and other 

 similar causes, will influence the effect that any particular game 

 or amusement will have upon him ; and in the exercise of a sound 

 common sense, by himself and his friends, he will select and vary 

 his amusements as carefully as he selects his various occupations, 

 or chooses his diet. 



-»♦» 



DRIFT-SANDS AND THEIR FORMATIONS. 



FIVE large sand-tracts may be designated in Europe — the Ger- 

 man lowland, extending from Holland through Germany to 

 Russia (about 340,000 English square miles in area) ; the Dano- 

 Germanic island plains (20,000 square miles), including Schleswig- 

 Holstein, Denmark, and Jutland ; the Austro-Hungarian Danubian 

 plain (about 42,000 square miles) ; the Landes of France (about 

 5,400 square miles) ; and the sea-coast sands of Russia, Germany, 

 Belgium, Holland, and France. These extensive regions have, for 

 the most part, either been made amenable to cultivation, or at least 

 protected from the assaults of the winds by preservative planta- 

 tions. Tracts of this sort are often much more fruitful than we 

 are accustomed to suppose them to be. But there are also in Eu- 

 rope large fields of sand which are hardly if at all covered with 

 plants. They are the dunes and sands on the coasts of Prussia, 

 Pomerania, Jutland, many of the Danish and Frisian islands, 

 Hanover, Oldenburg, Holland, Belgium, and France. Large 

 systems of dunes extend in France from Brittany to near the Pyr- 

 enees. But there are also exposed sand-tracts in the interior. 

 The most extensive of them are in Hungary, of which the most 

 important is probably the sand-barren of the Banat. It forms an 

 oval about thirty-five kilometres long by eleven kilometres broad, 

 and has an area of nearly four hundred square kilometres. It 

 presents the appearance of a rolling region with elongated hills. 



