41 



quite pronounced in the boat at a firing distance of 800 to 1,000 

 feet, but not enough at twice that distance to damage any fitments 

 on the vessel, except possibly the bridge windows, which had been 

 opened. 



Results of mining and shell fire accomplished during the second 

 Tampa and second and third Modoc cruises were such as to indicate 

 that tliis form of attack on a sound berg can produce only a negligible 

 effect toward its disintegration. A few days after the charge had 

 been set off on the berg described a heavy fall of ice occurred by par- 

 tial disintegration of the top of the higher cliff whereby a mass of 

 broken ice was precipitated without warning into the sea in amount 

 estimated at around 20,000 tons. But when it is considered that a 

 berg of tliis size contains fully a million and a half tons, the amount 

 loosed is insignificant, granted that the mining was instrumental in 

 producing this slight disintegration. There must always be risk 

 from ice falls to the boat's crew working alongside any berg during 

 the breaking-up season when the patrol is being carried on and, as 

 has been said, the good results obtained are not commensurate with 

 this risk. 



An interesting temperature effect was noted at certain times when 

 the vessel steamed under the lee of the high wall of the berg named. 

 With a southerly wind (SE., S., and SW.) blowing, and the air tem- 

 perature away from the berg as registered on the vessel at 44° F., 

 immediately under the lee of it, in the williwaws set up, the thermom- 

 eter would rise to 48° or 50°, a change quite noticeable physically, 

 as well. The eddy from the berg summit had drawn down the 

 warmer air of the stratum above. 



The continued observation of tliis berg from day to day afforded 

 a study of several features connected with the breaking up and ero- 

 sion of the ice mass under the influence of warmer air currents and 

 sea water. As a general proposition, it appeared that loss from 

 simple melting goes on at a liigher rate in the underwater body of 

 the berg in water between 42 and 52°, which was the range experienced, 

 than in the exposed portion with the air temperatures about the 

 same or a little higher. The erosion at the water line, due to the 

 wave action in bringing uncooled water to the attack, goes on much 

 more rapidly than below, and the effect is a succession of undercut 

 water lines on the berg. 



But it was found that the reduction of the berg proceeded much 

 more rapidly by another action than that of melting; and this, the 

 disintegration by the spawling off of fragments of greater or less 

 magnitude, due to temperature strains and seepage of the water from 

 melting ice through the strain crevices, which tended to loosen the 

 hold of the fragments on the main mass. Consequently, there was a 

 continual emergence of the berg from the sea, due to the lightening 

 effect of the losses above surface. It was seen that within 10 days 



