My dearest Father,

My new pendulum apparatus works very successfully. It is very easy to keep the pressure at an inch and a half for any length of time, and the pendulum swings for 24 hours. I have swung it down in the tunnel for 3 days & nights without stopping setting it agoing as soon as the arc became very small & side by side I had my silver pendulum swinging in air the whole time. But as there were occasional slight blasts which approached my station until one finally broke my spring governor I am going down again when all the blasting has ceased & then I shall first have one pendulum swinging below & the other above & then I shall change them. Only I cannot in that proceeding keep up the work so long because I haven’t the force in my party. It was very hard work

My balance experiment seems to be a complete failure. The balance won’t turn with the long wire attached. It seems to stick. I cannot understand it. I cannot see how there can be any obstruction in the box but I shall let down a block which fits it so as to clear everything out. But I think it is the spring of the wire which prevents any impulse being communicated. Thus, you pull the upper end of the wire and I suppose it sets up vibrations of elongation & contraction in consequence of which the wire becomes a little elongated permanently & the weight at the bottom is not affected or you push the upper end & it becomes a little contracted. It is a copper wire. Perhaps a steel wire would not act so. My hypothesis is contrary to the doctrine that substances are perfectly elastic within a certain range but I think I am right.

If I find there is nothing in the box I must be right. The accuracy of discontinuous laws should always be suspected. I have had a good deal of trouble in my camp this summer. McClintock behaved badly at one time but since receiving a sharp admonition from Capt. Patterson he has turned over a new leaf. Edmund has left & I have Willie Winlock for the summer. He does beautifully. Frank the stable boy did tolerably until one day after a very mild reproach he took his departure with much impertinence. The fact was he didn’t have enough work to keep him satisfied.

The weather has been extraordinarily bad. Rain all the time. I like Patterson in my new relation to him very much. With his consent I have ordered a Thomas’s Arithmometer which adds to any number 10ⁿ times any other so that aA+bB+cC+etc. are very easily calculated. The factors run to eight places of decimals & the result to 16. I work the most favorable problems at least 5 times as fast as a computer and

I envy Jem being in Europe with you and Mother. Mother is so particularly adapted to enjoying everything. I don't think those rooms in Clarges Street were 6 guineas when I was there but that was not in the season. It is about what you would pay at Miss Upham’s.

I am very glad you have got the clock although from what you and mother say I imagine you paid too high for it. Winlock’s only cost 10 pounds & I fear yours was 50. I wish now you are there you could stay all winter & take Mother to Italy. I know she would enjoy it so much.

I wish we could all be abroad together in the spring.

With dearest love to Mother & also to Jem,