ice during January and February.

Fogs.--Fogs are most frequent along this part of the Atlantic coast during the months of December, January, and February, but may be met at other times during the year. Easterly winds bring them and westerly and northerly winds clear them away. In the late fall dense fogs are liable to occur and may last during forenoons for 2 or 3 days in succession. Autumnal fogs nearly always clear up before noon. It should be noted, however, that fogs are less prevalent along this part of the Atlantic coast than they are farther north. At Wilmington, Del., there was an annual average of 373 hours and 23 minutes of fog during the 24-year period 1922-45. At Fort Mifflin in the harbor of Philadelphia, fog signals were operated 171 hours per year, averaged over the period 1939-46.

Precipitation.--There is no rainy season. The mean annual precipitation

at Philadelphia over a period of 75 years was 40.41 inches. The mean annual precipitation at Wilmington, Del., over a period of 25 years was 43.05 inches.

Temperature.--At Philadelphia the mean maximum temperature over a period of 73 years was 62.3 degrees Fahrenehit and the mean minimum temperature was 46.6 degrees. At Wilmington, Del., the mean maximum temperature averaged 63.7 degrees Fahrenheit per year and the mean minimum temperature averaged 44.45 degrees over a period of 25 years.

The following table of meteorological data for Wilmington, Del., which is representative of conditions at localities below Philadelphia, was furnished by the Chamber of Commerce and the Street and Sewer Department, Wilmington, Del. The table for Philadelphia, which shows the conditions generally prevailing at the localities above Philadelphia, was furnished by the Weather Bureau, Department of Commerce.

Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec. Annual

Daily mean maximum temperature, degrees Fahrenheit, for 73 years 39.5 40.9 48.6 60.9 72.0 80.4 84.6 82.5 76.0 65.9 52.6 42.8

62.3

Daily mean minimum temperature, degrees Fahrenheit, for 73 years 25.7 26.9 33.0 43.3 53.8 33.0 43.3 53.8 62.4 67.8 67.1 60.0 49.7 38.8 29.8

46.6

Meteorological Data for Philadelphia, Pa. (Cont'd)

Apr. May June July Aug. Sept. Oct. Nov. Dec. Annual

Jan.

Feb. Mar. Apr.

3.30 3.32 3.39 3.05 3.26 3.24 4.15 4.62 3.14 2.81 2.70 3.43 40.41

Hours of operation of fog signals at Fort Mifflin, 1939-1946

There are no existing bridges across the Delaware River below Philadelphia. Plans have been formulated and a permit has been issued for the construction of a high-level fixed span bridge to cross the Delaware River between Pigeon Point at Wilmington, Del., and Deepwater, N. J. Mantua Creek at Paulsboro, N. J., is crossed by two bridges. Three bridges cross the Delaware River connecting Philadelphia Harbor with the localities across the river and one connects the city of Camden with Petty Island. Above Philadelphia one bridge connects the cities of Burlington and Bristol. There is also one bridge at the terminus of the 12-foot channel at Trenton, N. J. The table on page 17 gives full details concerning the location and description of the bridges across Mantua Creek and

the Delaware River.

Bridge Regulations

Regulations governing the operation of the bridges over the Delaware River are quoted below. These regulations also pertain to the bridges over the Schuylkill River in Philadelphia Harbor, which are described in Port Series No. 7, covering the Ports of Philadelphia, Pa., and Camden, Gloucester, Delair, and Riverton, N. J.

1. Signals.-When at any time during the day or night any vessel, tug,

1.68

New Jersey State Highway Bridge, Paulsboro, N. J.

Vertical

75.0

69.0 (1)

64.0 (1)

lift

Delaware River (2)

Petty Island.

or other water craft unable to pass under the bridge approaches it with the intention of passing through the draw, the signal for the draw to be opened shall be three blasts of a whistle or horn blown on the vessel or craft.

If the draw is ready to be opened immediately when the signal is given on the vessel or craft, the signal shall be answered immediately by two blasts of a whistle or horn blown on the bridge; and if the draw is not ready to be opened immediately on the signal being given on the craft, the signal shall be answered immediately by one blast of a whistle or horn blown on the bridge.

2. Opening the draw.-Upon hearing or perceiving the prescribed signal, the bridge tender shall immediately clear the draw span and open the draw to its full extent for the passage of the vessel or other craft: Provided, That the draw of a railroad bridge need not be opened when there is a train in the bridge block approaching the bridge with the intention of crossing, nor within five minutes of the known time of passage of a scheduled passenger, mail, or express train; but in no event, except in case of breakdown of the operating machinery, shall the opening of the draw be delayed more than five minutes in the case of a highway bridge, nor more than 10 minutes in the case of a railroad bridge: And provided further, That the draw need not be opened for the passage of a tug or other craft equipped with a movable stack or mast which can readily be lowered so as to permit its passage under the closed draw, unless such craft has in tow a vessel which is unable to pass under the closed draw, or by reason of stress of weather it is unsafe to lower such stack or mast.

3. Interference with operation.-Vehicles, street cars, locomotives, and trains shall not be stopped on the draw spans, nor shall locomotives or trains be stopped in the bridge blocks of railroad bridges in such manner as to delay the operation of the draw, except in case of urgent necessity; nor shall vessels be moored to the bridge fenders or so maneuvered as to unnecessarily hinder or delay the closing of the draw; but all passages over, through, or under the bridges shall be prompt, to avoid delay to either land or water traffic.

4. Hinged stacks and masts.--Each tug, towboat barge, and other small craft regularly and habitually navigating the Schuylkill River shall be subject to inspection and measurement by The District Engineer, Philadelphia District, Corps of Engineers, in charge of the district, to determine the exact height above the water surface of its pilot or deck houses, when such vessel is in its ordinary trim; and the said district engineer is hereby empowered to decide in each case, whether or not the vessel shall be equipped with hinged or removable stacks, masts, and flagpoles, which can be lowered to enable the vessels to pass under the closed draw of any or all of the bridges. If the district engineer decides that such action should be taken, he shall notify the vessel owner and the bridge owner of his decision, specifying a reasonable time for making the alterations; and after the expiration of the time specified, the draw need not be opened for the passage of such vessel unless it has in tow a vessel unable to pass under the closed draw, or by reason of stress of weather it is unsafe to lower such stack or mast.

5. Operating machinery.-All drawbridges to which these regulations apply shall be equipped with adequate quick-operating power machinery for opening and closing the draw, and this machinery shall at all times