The disposition of the mountain ranges in parallel chains affords space for the development of streams both in Luzon and Mindanao.  The larger islands contain inland seas, into which pour countless small streams from the inland hills.  Many of them open out into broad estuaries, and in numerous instances coasting vessels of light draft can sail to the very foot of the mountains.  Rivers and inland lakes swarm with varieties of fish and shellfish.  By reason of Spanish restrictions, but little can be said as to the character of the stream banks and beds.  Four of the rivers are navigable, and, by the statements of those who have spent some little time on the islands, most are fordable.  Drinking water is obtained by many of the towns from the rivers at points just above tide limits, and the water is said to be good.  Bridges are few and crude, but are generally built to withstand heavy strain.

The island of Luzon abounds in rivers and streams.  The following are the principal water courses: 

Rio Grande de Cagayan, the source of which is in the northern slope of the Caraballo Norte.  It has numerous affluents, among others the Magat and Bangag, and, after a course of about 200 miles, falls into the China Sea in the vicinity of Aparri.

Agro Grande starts in the north, in the neighborhood of the ranch of Loo, receives the affluents Tarlag and Camiling, as well as many others, has a course of about 112 miles, and falls into the Gulf of Lingayen.

Abra has its origin on the opposite slope to that where Agno Grande takes its rise; runs for about 87 miles, and, after receiving the affluent Suyoc, divides into three arms and falls into the China Sea over the sand bars of Butao, Nioig, and Dile.

Rio Grande de la Pampanga is called Rio Chico up to the lake of Canasen, near Arayat, where it changes its name after its junction with Rio Gapan.  Its course is a little over 38 miles; it receives the Rio de San Jose and divides into a multitude of arms as it falls into the sea to the north of Manila Bay.

Rio Pasig has its source in the Bay Lagoon, and falls after a course of 19 miles into Manila Bay.

The military notes on the climate of the Philippines, the official record of the temperature and the gales and typhoons, and directions regarding the handling of ships in the peculiar tempests that prevail at certain seasons around the islands, are of absorbing popular interest, and of striking special usefulness.

Climate.—­In the region of Manila, the hottest season is from March to June, the greatest heat being felt in May before the rains set in, when the maximum temperature ranges from 80 degrees to 100 degrees in the shade.  The coolest weather occurs in December and January, when the temperature falls at night to 60 or 65 degrees, and seldom rises in the day above 75 degrees.  From November to February the sky is bright, the atmosphere cool and dry, and the weather in every way delightful.  Observations made at the Observatortio Meteorologico de Manila have been compiled by the United States Weather Bureau, covering a record of from seventeen to thirty-two years, from which the following is an extract: