TIDES AND CURRENTS IN BOSTON HARBOR O 



The reading point upon this new gauge is so placed that the heights will corre- 

 spond with those upon the staff gauge heretofore used. 



The observer may always keep his gauge rod dry and thus prevent changes of 

 float line. 



Cost of above, exclusive of expenses for traveling and subsistence of builder, $42. 



The self-registering gauge to which reference is made in the pre- 

 ceding description was a gauge that had previously been installed by 

 A. Boschke, for the harbor improvement commission of Boston. 

 This gauge was placed in charge of the same tide observer who read 

 the Coast Survey tide gauge. 



The box gauge, like the previous staff gauge, was read by the tide 

 observer every five minutes near the times of high and low water. 



Observations appear to have been continued with the box gauge 

 until the series was temporarily stopped, September 30, 1866. 



ReestaUisJiment of station witli self-registering gauge.— On August 15, 

 1867, the tide station was reestablished and a self -registering gauge 

 was installed at the dock next southwest of the dry dock, A. C. 

 Mitchell having charge of the installation. Mr. Mitchell was in- 

 structed to put up a staff for comparative readings and also a box 

 gauge. 



The observer first placed in charge of the self-registering gauge 

 when installed in 1867 was C. Levin, who served until September .3, 

 1867, and was succeeded by Henry Howland, who continued in 

 charge until the end of the series, in 1877. 



EstahlisJiment of new lench marTc. — When the self -registering gauge 

 of the Coast Survey was installed in August, 1867, A. C. Mitchell 

 reported "The old bench mark does not exist, the dry dock having 

 been rebuilt." Mr. Mitchell presumably considered the relaying of 

 the stones as equivalent to the destruction of the old bench mark 

 and established another bench mark near the upper end of the dry 

 dock on a section that was built about the year 1859, the dock being 

 lengthened about that time. 



This mark, now designated as "B. M. 2," and originally referred to 

 as the "new bench mark," was described as "the top of the facing of 

 the dry dock on the west side and near the head directly over the foot 

 of the long steps and is designated by an arrowhead cut in the side 

 of the stone." A spike driven into a spile directly in the rear of the 

 tide house and corresponding with the 18-foot mark on the staff was 

 1.433 feet below the new bench mark, thus making the new bench 

 mark 19.433 feet above the zero of the tide staff. 



In the following year Mr. Mitchell connected the new bench mark 

 with the point on the coping previously used as the old bench mark and 

 ascertained that the new bench mark was 0.176 foot lower than the old 

 one. The zero of the new staff was therefore approximately 19.61 feet 

 below the old bench mark, assuming the elevation of the coping had 

 not been materially changed. 



Pressure gauge. — In the latter part of the year 1869 a pressure gauge 

 designed by John M. Batchelder was installed for experimental pur- 

 poses, the regular gauge being continued in operation. The pressure 

 of the water was transmitted through a rubber bag filled with glycerin, 

 and the rise and fall of the tide was automatically registered in the 

 form of a curve similar to the curve from the regular gauge. In the 

 records it was called the "glycerin gauge." It was retained in use 

 until February, 1872. The records from this gauge are not used in 

 this publication. 



