• Chandler is living in Washington from at least 1854 to 1861.
  
• December 22, 1854: Chandler is going to Philadelphia for the holidays to join his father, "who is our ambassador to Spain". (page 30) The US Ambassador to Spain at that time is Pierre Soule, but I can find no record of him having a son named Chandler or of any Chandler Soule.
  
• April 6, 1858, page 85: Chandler is to attend Mrs. Senator Gwin's fancy dress ball on April 9, 1858 costumed as Sir Walter Raleigh. I have checked the NY Times article of 4-12-1858 about the ball, and neither Chandler nor Sir Walter Raleigh is mentioned.
• July 1, 1858: Chandler is going to South America (page 88).
• Entry for April 22, 1861, page 151: Chandler joined the Federal Army, commissioned as a 1st lieutenant.
• Entry for June 19, 1862, page 200: Chandler was in the hospital in Fredericksburg severely wounded.
• July 21, 1862, page 205: Chandler is still desperately ill.
• August 2, 1862, page 206: implies that Chandler died. If he died in Fredericksburg, it is possible he is buried there in the National Cemetery. No person with the given name Chandler appears on the list of Union soldiers buried at the Fredericksburg National Cemetery.

Does anyone have any idea who this Chandler is?

The following is from A Belle of the Fifties by Virginia Clay-Clopton. She doesn't give a date, but the event clearly took place before June 1861. "Professor" Maury (she seems to have forgotten his full name, Matthew Fontaine Maury) was still the director of the Naval Observatory in Washington at the time of the visit she describes. I find her description of Mr. Maury rather unkind.

I remember an amusing visit paid by a party from our mess to the observatory of Professor Maury. It was an occasion of special interest. Jupiter was displaying his brilliancy in a marvelous way. For no particular reason, in so far as I could see, the Professor's great telescope seemed to require adjusting for the benefit of each of the bevy present. I noticed Professor Maury's eye twinkling as he went on with this necessary (?) preliminary, asking betimes: "What do you see? Nothing clearly? Well, permit me!" And after several experiments he would secure, at last, the right focus. When all of his guests had been treated to a satisfactory view of the wonders of the sky, Professor Maury delivered himself somewhat as follows:

"Now, ladies, whilst you have been studying the heavenly bodies, I have been studying you!" and the quizzical expression deepened in his eye.

"Go on," we assented.

"Well," said the Professor, "I have a bill before Congress," (mentioning its nature) "and if you ladies don't influence your husbands to vote for it, I intend to publish the ages of each and every one of you to the whole of Washington!"