6 The whole upper part and ceiling of the room were lined with a tent-lining of thin drilling. On three sides the room is double walled and covered with Cabot sheathing and asphaltoid roofing paper, except for a window 10" X 10" in size in the N. W. wall. Partition forming SW side is of single boards, separating room from rest of shed. Mr. Mac Millan determined merid- cian across middle of space chosen for seismograph by means of a first class theodolite transit. We marked the line with a cord stretched between nails driven into the walls where the meridian intersected them, the point being located with the telescope - When the frame was set up, I got the outer edge of the N-S arm parallel to the cord within less than 1/8 inch, measuring with a carpenter's jointed wooden two-foot measure. Balanced the heavy mass in an- stable equilibrium, secured it thus with the centering setscrews, connected the thrust arms with the needle arms and loosened the setscrews - Packed a Weather Bureau stan-