6 KANSAS CITY REVIEW OF SCIENCE, 
years, 1-30; Hind gives it 1-51; and Main 1-62. Bessel merely decided that it 
was too small for measurement with his heliometer. This discordance shows 
quite clearly the difficulty of measuring such a bright glowing disc as that of the 
planet Mars. 
IN GUN aeNGe 
COMPARATIVE MERITS OF WOOD, STONE AND ASPHALT 
PAVEMENTS. 
GEN. Q. A. GILMORE, U. S. A. 
Assuming the foundation to be firm and solid, so that ruts and depressions 
cannot form upon the surface except from actual wear, a pavement of stone 
blocks, of first quality as regards hardness and toughness, will possess the long- 
est life of the three, and one of wood blocks the shortest; asphalt lies between the 
two and very near to the stone, and will fluctuate from this position with the 
amount and kind of traffic, and the influences of the climate. Asa rule wood 
must be regarded as the least durable. When it begins to go—at the end of two. 
or three years, under heavy traffic—it wears rapidly into deep and numerous ruts, 
by the crushing of the blocks to their entire depth. Unless the stone be of ex- 
cellent quality for pavements, it takes the second place in the order of durability, 
and asphalt the first. 
The absolute cost of constructing the different pavements will of course vary 
very considerably with the locality. It is believed, however that with few excep- 
tions, the following order of cheapness will obtain throughout the United States : 
viz., first, wooden blocks; second, asphalt, on a solid cobble stone foundation ;. 
third, asphalt on a concrete foundation ; fourth, stone blocks on a concrete found- 
ation. 
Under the head of cost and maintenance of repairs, the life or endurance is. 
to be considered, and the total expense must extend over and cover a period of 
time representing that endurance, under the assumption that at the end of that 
period, the pavement is in as good a condition as at the beginning when it was 
new. The repairs for the first two or three years will be comparatively trifling, 
and in some cities, more especially in England, it is customary for the constructor 
to maintain the pavements in a good sound condition without charge for one, 
two and sometimes three years, and subsequently for a longer period, seldom ex- 
ceeding fifteen years, for a specified sum per square yard per year. 
With regard to wood and asphalt, the recorded observations make it certain 
that although a pavement of wooden blocks is less costly to construct than one of 
asphalt, not only is its annual cost for repairs greater, but its mean annual cost 
during its life, inclusive of the first cost, is also greater than that of asphalt. With 
