|Braun is continuing his labours with zeal after Boys's help. The arm measurements must be done again, because the micrometer was faulty and must be sent back to the maker. Notes that he forwarded a letter to Prague for Boys although the letter was accidentally opened. He thinks that Boys will have seen Professor Mach's photographs of flying projectiles while in Prague. The observatory director there, Weineck, is very kindly. Braun wishes to measure the strength of the quartz fibres supplied by Boys - his measurements of their thickness mostly agrees with those of Boys.