158 ANNUAL OF SCIENTIFIC DISCOAXRY. 



On the 29tli of last December, when but a very limited supply 

 of water could be obtained, divers went down, examined the 

 strainer, and found that it and its surrounding piles were one 

 mass of ice particles collected into a mound some 10 feet high and 

 about 15 feet in diameter, and that large quantities of minute 

 crystals of ice were rapidly passing and adding to the mass already 

 collected. Specimens of the ice were brought to the surface in a 

 bag. It was in sheets and particles thin as paper, translucent, 

 with sharp, pointed edges. A further examination developed the 

 fact, that the small amount of water the pump was then receiving 

 came through the lower or down-stream side of the strainer, this 

 being the only point where the diver could approach it, and which 

 was found but slijchtlv covered with ice. Having ascertained the 

 existing state of affairs, the commissioners felt confident that a 

 remed}^ could now be provided, and with a large piece of canvas 

 they bad the strainer completely covered and encircled, except on 

 the down-stream side ; but temporary relief only was afforded by 

 this expedient, and another descent to the strainer was under- 

 taken. The diver went down and found out this very important 

 fact, that, with the temperature of the atmosphere at 29'', the 

 water at the surface was 33°, while at the bottom of the river it 

 was 35°. At this descent much less ice was found on the strainer 

 and its surroundings than at the first time. The lower side was 

 clear, but on the upper side the action of the ciUTent had worn the 

 ice into elongated cones, pointing up stream. At this time the 

 pump was receiving a full supply of water. About 3 hours later, 

 the diver again descended (thermometer 33°) ; he found the ice 

 had entirely disappeared. The wooden platform was removed, 

 since which time no trouble was experienced, until the surface ice 

 of the river began to move, when there were a few hours durins; 

 which no water could be obtained; but with this exception no fur- 

 ther delays have since occurred. 



It is clearly proved that ice particles are ever present in the 

 river, and are continually passing down b)^ the action of the cur- 

 rent, collecting upon whatever obstructions they happen to meet 

 with in their passage. The commissioners, therefore, advise the 

 entire removal of all spiles and other substances adjacent to the 

 strainer, believing that with nothing but the smooth dome of the 

 strainer for these particles to lodge upon, the quantity that will 

 accumulate cannot very seriously prevent the flow of water to the 

 inlet J3ipe. — Scientific American. 



FINDING THE DEVIATION OF THE COMPASS. 



The *' Mechanics' Magazine" describes an invention designed 

 to simplify the process for finding the error on the common steer- 

 ing compass, or, in other terms, the deviation of the magnetic 

 from the true meridian. It has been patented by Major-General 

 Shortrede, of Lee, who attains his object by making some addi- 

 tions to the steering compass as usually made, l)y which it becomes 

 virtually an azimutli compass, vvithout interfering with its ordinary 



