Discusses advantages and disadvantages of 24 versus 36 hour series in meteorological observations. R.S.L. officially endorses 24 hours, but AQ should continue 36 hours if best for him. Does not possess the Comptes rendus of French Institute and cannot therefore see No. 413. Will attempt to procure sight of it. Asks AQ to return [P. F.] Verhulst's work to him. Expresses respect for AQ's work. Asks for understanding if JH does not answer every letter promptly.