East winds are prevalent generally in April, May, and June, but sometimes continue right through the summer, but for the remainder of the year, often for many weeks without change, south-west wind keeps in possession.
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Fig 5a. Living model illustrating principle of the forth bridge.
On three or four days during the year gales blow with such violence as to stop even large paddle boats from attempting the passage. On many other days the smaller barges and launches have to keep within shelter. During such times all outside work was necessarily stopped owing to the impossibility of handling material by the derrick cranes, or of getting about on the exposed stagings. From twenty-two to twenty-three full working days in the month must be considered very satisfactory in this climate; on many days only an hour or two need have been lost but for heavy rains in the early hours, which drenched the men and sent them to their homes. When such happened no power of persuasion was great enough to bring them back to work again, even if the weather turned fine and continued so for the rest of the day—a curious fact not easy of explanation.
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Fig 10. Map of the firth of forth.
Of snow there was but little during the seven winters, and but few days were lost through its covering the ground, but the frost caused much stoppage in a work where hydraulic appliances were so largely used, and where, owing to the enormous extent to which pipe leads had to be carried, it was impossible to effectively protect them all. It was thus the practice to break a number of joints and allow all pipes to drain dry after work stopped at night. Some of those joints were on deck, others on the very top of the structure, and a fire which occurred one night, February 13, 1889, on Inchgarvie spread to an alarming extent, and might have had most serious consequences to the lower portions of the steelwork as well as to the granite piers before the joints could be closed and the pumps made effective. The danger was all the greater that a furious gale was blowing from the south-west, which made it a matter of some danger to get to the island at all, or when there to ascend to the top of the superstructure to find the broken joints.
The variations in temperature are not excessive, and may be said to range between 20 deg. Fahr. and 85 deg. Fahr. minimum and maximum in the shade respectively.
Far greater than storms to the sailing craft passing the bridge is the danger from sudden calms which frequently occur during spring tides when a strong ebb is running, and which cause them to drift about helplessly in the powerful currents. At such times the barges and launches belonging to the works were on the look-out to run to the assistance of any shipping becalmed and tow them into mid-channel. To ward off all craft from the iron staging on Inchgarvie, where they would certainly have come to grief, but where they also might have done considerable injury to the structure in the early days
