TIDES AND CURRENTS IN BOSTON HARBOP d 



Tide observers. — The first staff readings were taken by Isaac 

 Williams, a sergeant in the Marine Corps, who served as tide observer 

 from the beginning of the series in 1847 until the time of his death on 

 August 14, 1857. He was succeeded by his son-in-law, T. E. Ready, 

 who served until the station was temporarily discontinued in 1866. 



Letter from tide observer. — The following is a copy of a letter written 

 by Mr. Williams in 1857, apparently in reply to inquiries from the 

 office: 



Charlestown, Mass., July 9, 1S57. 

 Capt. M. L. Smith, 



Assistant in charge Coast Survey Office, Washington, D. C. 



Dear Sir: Yours of the 7th instant has just been received, and I hasten to 

 answer the question asked therein. 



1. "Have the tides been observed at the same spot and the same gauge?" 

 The wall of the dry dock has settled some 4 or 5 inches; there is a difference of 

 2 inches in some of the feet, say from 20 to 22 feet. The foot will measure near 

 14 inches, while in some other feet the measure is nearly right. I have within a 

 short time taken the observation a short distance below, I have taken particular 

 notice that it did not vary a moment in time or measurement. 



2. The time is kept by a rather poor watch which I keep regulated by Cam- 

 bridge time. I have used the same watch, or rather the same time, for a number 

 of years. I have made appUcation to Mr. Mitchell to purchase a good one 

 warranted from 1 to 10 years. Hope you will use your influence in getting the 

 permission to purchase. 



3. My work of observing has been always the same. 



4. I am not aware that there has been any change in the depth of the water 

 near the gauge or in the channels leading to it. I never look at the difference 

 between mean and apparent time but take my observations every 5 minutes, 30 

 minutes previous to high and low water. When the last 5 minutes expire I wait 

 until the water begins to rise or fall; I then note (after stopping 5 minutes) the 

 first rise or fall and then in 5 minutes more make another observation and leave 

 until half an hour of the next tide. 



Yours truly, 



(Signed) Isaac Williams. 



Expansion oj seams in dry dock. — From the above letter it appears 

 that in 1857 the seams between the stones had opened by a very 

 noticeable amount, although it is possible that the excess of 2 inches 

 noted by Mr. Williams may have been estimated by eye rather than 

 obtained by direct measurement. Mr. Williams attributed these 

 openings to a settlement of the dock, but from later investigations, 

 especially those of John R. Freeman, chief engineer of the committee 

 on the Charles River Dam, it appears more probable that they resulted 

 from the action of frost in raising the stones above the seams. 



Change oj location oj staff. — Some time in 1857 the place of taking 

 the observations was changed from the entrance to the dry dock 

 to a point about 400 feet easterly, and it is possible that the state- 

 ment in Mr. Williams's letter that he had "within a short tirne 

 taken the observation a short distance below," had reference to this 

 change. He adds that he had "taken particular notice that it did 

 not vary a moment in time or measurement." Just how the staff 

 in its new position was set to agree with the old tide scale is not 

 known, possibly by water-level comparisons. 



Repairs to dry dock. — It appears that about the year 1859 the dry 

 dock was lengthened by extending the inner end and that other 

 repairs were made. References to these repairs are contained in a 



