40 REPORTS ON THE STATE OP SCIENCE. 



was pointed north or towards the advancing and retreating tide; the 

 resulting photograms are practically straight lines. 

 These observations were discontinued on May 24. 



VII. Tidal Load Experiments in Pennsylvania Railway Tunnels. 

 Since 1909 a number of experiments have been made regarding the 



stability of the Pennsylvania Eailway tunnels under the North or 

 Hudson Eiver. The results show that the tunnels rise and fall under 

 the influence of the superincumbent tidal load. A 4.4-foot tide causes a 

 variation in elevation of 0.008 feet. 



This was arrived at by sinking a tube in certain instances to a depth 

 of 200 feet through the silt beneath the bed of the tunnel until it reached 

 the solid rock. A 2-inch iron rod passed freely down each of these tubes 

 and was firmly fixed in the rock. The upper end of the rod passed 

 through a stuffing-box on the top of the tube. The assumption made 

 was that the top of this rod remained fixed and relatively to it the bottom 

 of the tunnel rose and fell. This relative movement was recorded by a 

 lever having a multiplication of ten which recorded on a strip of paper. 

 The resulting diagrams have an exceedingly regular character and corre- 

 spond in time with the records of a tide-gauge which gives the height of 

 water in the river. The tunnels are resting in a quasi-fluid material and 

 show slight depressions by the passing of locomotives. A load passing 

 through the tunnel causes a wave-like action, a point immediately 

 beneath the load being depressed, whilst the point 200 feet in advance 

 of the same rises. I am indebted for this information to Mr. Forgie. 

 Engineer to the North Eiver Division. 



VIII. Experiments in Pits in the Midlands. By J. J. Shaw. 

 The experiments commenced at the end of June 1910 by the in- 

 stallation of a horizontal pendulum in a chamber 1,960 feet below 

 ground at the Sandwell Park Colliei*y, near West Bromwich. The 

 instrument used was similar to the one used at Bidston, but with facili- 

 ties for obtaining a somewhat higher degree of sensibility. The chamber 

 was lined with several feet of concrete, but unfortunately the traffic 

 of the pit passed within a few feet of it, whilst at a distance of about 

 100 feet there was a large sump from which water was pumped every 

 night. From the outset it was seen that the strata were ever moving, 

 the movements being partly due to pumping, blasting, and traffic. The 

 direction in which the boom wandered was towards the dip of the 

 strata. Observations were discontinued early in August, and the instru- 

 ment was removed to a new collieiw at Baggeridge, near Dudley, seven 

 miles from its previous position. The instrument was installed at the 

 end of a concrete-lined cul de sac, where only occasionally traffic passed^ 

 and then never nearer than 100 feet. The depth was 1,800 feet. 

 Pumping took place once a month. The movements were very similar 

 to those at West Bromwich, and there was a tendency for the boom to 

 wander in the direction of the dip. In this instance this was towards 

 the west, whereas at West Bromwich it had been towards the east. 

 The outstanding feature of these experiments is that even at very con- 

 siderable depths observers will not be immune from continual changes 

 of level. In the early part of this year the rate of the film was changed 



