TUTTLE ENGINEERING NOTES ON HAWAII. 135 



longest of these dates back to 1874 without interruption. Although 

 separated by small distances, they show a variation in the average 

 annual record ranging from 22.94 to 39.53 ins. 



In a recent article on " Meteorology in Hawaii," by Professor 

 Curtis J. Lyons, Territorial Meteorologist, it is stated that the mean 

 annual temperature at Honolulu is 74, with an annual variation of 

 not more than , and that there is a probability that no point on the 

 coast has a temperature of more than 1 lower. The average monthly 

 variation at Honolulu is from 70 in January to 78 in July and 

 August, with an extreme monthly range of from 54 to 88 and a 

 daily range of from 50 to 90. With increase in elevation on the 

 islands there is a fall in temperature, probably averaging 1 per 300 

 ft. The percentage of saturation or humidity at Honolulu averages 

 72 per cent. 



This delightful climate is due to the position of the Islands with 

 reference to the return polar currents, the trade winds, which blow 

 over them, prevailing at the islands for about 270 days per year. 



Applying the rule of decrease of temperature with increase in ele- 

 vation, it will be noted that temperatures below freezing might be 

 expected at the higher elevations on Maui and Hawaii, and on the 

 latter island snow caps can usually be seen on the crests of Mauna 

 Kea and Mauna Loa. 



The Soil. The geological structure of the islands is entirely of 

 basalt. The volcanic agency by which they were formed seems to 

 have first manifested itself at the northerly end of the group, where 

 the old craters are difficult of definition; the action has now ceased 

 at all of the islands except Hawaii, the largest and southernmost. 

 Here there are two volcanoes, Mauna Loa and Kilauea, which are 

 periodically active; at the latter there is always more or less evidence 

 to show that the quiescent stage may be but a brief one. It is prob- 

 able that the seaward slopes from the craters were originally about 

 uniform, and ranged up to, perhaps, 1.5%, but the heavy rainfalls on 

 the summits have caused more erosion here than at the coast, cutting 

 away the surface and furrowing it with deep gulches, and, finally, as 

 on Oahu, reducing the junction of the opposite sides of the tops of 

 the craters to a ragged knife-edge or saw-tooth appearance. 



The disintegrated material of the higher elevations is washed 

 downward and deposited on the lower slopes, producing here a deeper 



