Letter from J [John] Herschel, Brompton Barracks, to 'Dear Mama' [Margaret Brodie Herschel] They may have been wondering about his silence, which he explains by his business. He has been on rifle drill and pactice, which was very tiring. He has had two days of pontooning, making bridges and rafts. He gives illustrative sketches. He is on Rochester Barracks duty tomorrow. He has news for the children in the shape of many moths and butterflies. 22 July 1857