408 TRANSACTIONS OF THE 



This leaves Oakland and the slope of which I have spoken in a triangle. 

 Consider the triangle standing vertically. The hill barrier to the east 

 would lie behind the imaginary upright line of the triangle ; the land slope 

 would be its base line, and the path of the ocean breeze would be the upper 

 line of the triangle, or its hypothenuse. In this triangle the air is free from 

 fog, and moves gently eastward with just enough motion, bracing coolness, 

 and refreshing stimulus to make the temperature delightful, life comfort- 

 able, and healthfulness certain. No sanitary department elsewhere can 

 ever do for any city what nature is steadily doing for the city of Oakland. 

 The fog clouds pass overhead at an elevation of from 500 to 2,000 feet. 

 This is nature's sunshade, catching the rays of the summer sun and casting 

 cool and grateful shadows on the land surface below, whilst it leaves that 

 surface free from wind and dampness. 



There is a horizontal triangle of protection also. At the Golden Gate, 

 this sea breeze can and does come in on the water level; but by reason of 

 the conformation of the hills, this tongue of wind becomes forked — one part 

 traveling northward and the other to the southeast. The small arrows 

 show the course and divisions of this lesser current. 



One part bears northward around the point of hills north of Berkeley; 

 the other bears southeast down the bay. The former is quite strong, the 

 latter rather weak. The reason for this is clear; the former runs in the 

 direction of the prevailing sea breeze overhead , and hence maintains its 

 velocity; the latter turns down the bay, almost at right angles with the 

 general overcurrent, and hence its force is dissipated and weakened. 



The forking of the Golden Gate current leaves Oakland again in the tri- 

 angle of repose. Of this horizontal triangle the base is at the hills to the 

 eastward, and the other two sides are the two forks of the Golden Gate's 

 current of wind. For these reasons, considering these two triangles, I 

 think I may justly say Oakland is in the triangle of peace. Under these 

 circumstances, it is not strange that strangers do not realize the fact that 

 there is such a marked difference between the climate of San Francisco 

 and that of Oakland. I believe these triangles furnish the solution of the 

 question. On this point, too, there is a singular little fact well worth con- 

 sidering. That is this: when water runs out of a waterspout or trough, 

 if the trough is uneven on the under side, some water drips or curls under, 

 while the main stream goes ahead. Just so in this case. 



The general front of the fog-bearing sea breeze bumps against and rises 

 over the uneven top of the San Francisco hills; a little of the wind curls 

 under at the uneven summit of the first row of hills, and bears down on 

 San Francisco. But this curling down of the cloud current goes no fur- 

 ther, practically. 



This curling down, and the two triangles of repose, account, in my judg- 

 ment, for the phenomenal fact that Oakland, only 6 or 8 miles from San 

 Francisco, has a climate so much more benignant, and as different as 

 though the two cities were a hundred miles apart. 



The views here given will account for the following facts: (1) Why a 

 stiff summer sea breeze bears down in the streets of San Francisco; (2) 

 why that wind brings fog down with it to the land surface there; (3) why 

 the waves on the bay of San Francisco run higher on the line extending 

 northeasterly from the inner face of the Golden Gate than elsewhere; (4) 

 why the summer wind is strong across San Pablo Bay and up the Straits 

 of Carquinez; (5) why Oakland has absolutely no fog down in her streets, 

 when it is down on the west side of the bay; (6) why there is no surface 

 trade wind at Oakland; and (7) why the fogs of the San Francisco penin- 

 sula become grateful clouds over Oakland and vicinity. 



