A PROPOSITION FOR AN ARTIFICIAL ISTHMUS. 477 



at all thus turning, as he expected, that island into an abode of 

 arctic snow and ice. 



Another feature of the case is the fact that the daily tides 

 would not be the same on the two sides of the dam. To the north 

 one could look clear out to sea over the Atlantic Ocean ; to the 

 south is about three hundred miles of practically inland water 

 before one gets out to the open ocean coast. The tides on the 

 open coast are about the same height and come at about the same 

 times south and north ; and at present, at any given point in the 

 Irish Sea, the height of the sea level at any time is determined by 

 the resultant of the tides from the north and south respectively. 

 The construction of a dam at the northern entrance would leave 

 the whole Irish Sea subject only to the influence of the tides from 

 the south, while on the north side of the dam the tide level would 

 be the same as that of other points on the open coast. Since, 

 now, it would take some time, probably several hours, for the 

 effect of the southern tide to reach the south side of the dam, 

 the tides on the two sides would be anything but synchronous. 

 When the tide was at its height at the north side it would be, 

 perhaps, half-way up on the south, and would be high on the 

 south by the time a considerable recession had taken place on the 

 north. This variation would have a most important bearing on 

 the working of the power machinery at the dam, because, instead 

 of the difference of level between the water on the two sides being 

 constant, and giving therefore a constant pressure, it would vary 

 so as to be at times greater and at times less than would be the case 

 if the effect alluded to did not take place. In order, therefore, to 

 supply an equable driving head to the dynamos, the turbine wheels 

 would have to be powerful enough to work up to the required ca- 

 pacity on the minimum difference of level. Since the power made 

 available by the dam would be remarkable for the vast volume of 

 water to be drawn on, rather than for great difference of level, the 

 interference of the tides in at times reducing this difference per- 

 haps considerably would be a matter of grave inconvenience in 

 the way of the successful operating of the power generators. 



THE system of school education, though judiciously criticised, is not regarded 

 in the paper of Prof. Glynn, of Liverpool, on excessive mental work and some of 

 its consequences, as being in a marked degree accountable for nervous overstrain 

 in childhood. The tendency to this effect is considered to be in a great measure 

 counteracted by the attention given to physical education and by the mental elas- 

 ticity natural to youth. More serious are the consequences entailed by close and 

 anxious application to duty of teachers and older students. As concerns the 

 adult population, the injurious influence of overstrain is most active in towns, 

 where the tension in the struggle for existence is greater and is associated with a 

 desire too easily gratified. 



