The original use of commas was preserved, except where explicitly noted below. The original spelling of "pourtray" was preserved. Both Roman and Arabic numerals are used to number the plates; the text was left as is. Preserved the non-standard order in the index, where U comes after V. Removed extra comma after "which" on page v: "about which the parts." Changed "Sideral" to "Siderial" on page vi: "Solar, Siderial, and Equal." Added comma after "Mrs. B." on page 9: "your assistance, my Dear Mrs. B., in a charge." Changed "errroneous" to "erroneous" on page 10: "an erroneous conception." Added comma after "Mrs. B." twice on page 23: "Yet surely, Mrs. B., there;" and "But, Mrs. B., if attraction." Added commas before and after "Mrs. B." on page 25: "Pray, Mrs. B., do." Changed "pullies" to "pulleys" on page 64: "a system of pulleys." Changed "plate 6. fig. 5" to "plate 5. fig. 5" on page 65 in the body of the text and in the associated question, to designate the correct figure. Changed "twelves" to "twelve" on page 65: "twelve times less." Changed "stream" to "steam" on page 66: "expansive force of steam." Changed "Pray Mrs. B," to "Pray, Mrs. B.," on page 68. Changed "nonelastic" to "non-elastic" on page 70: "non-elastic like water." Removed extra comma after "one" on page 73: "one would ultimately have prevailed." Changed "eliptical" to "elliptical" on page 73: "elliptical or oval orbit." Changed "eclipse" to "ellipsis" on page 73: "motion in an ellipsis." Changed "elipsis" to "ellipsis" on page 75: "but an ellipsis." Changed "fig. 4 plate 3" in the question on page 75 to "fig. 4. plate 6" to designate the correct figure. Changed "day-light" to "daylight" on page 77: "see them by daylight." Changed the second question numbered 40 to "41" from page 79. Changed "eliptical" to "elliptical" on page 83: "they were elliptical." Capitalised "Mercury" on page 83: "made upon Mercury." Added question mark on page 84 after "those beautiful lines of Milton." Removed repeated word, "it", on page 88: "provided it were steady." Changed "aeriform" to "æriform" on page 136 (in versions supporting full Latin-1 character set). Changed "atmospherical" to "atmospheric" on page 139: "the atmospheric air." Changed "rarifies" to "rarefies" on page 140: "heat rarefies air." Changed "to day" to "to-day" on page 157: "our lesson to-day." Changed "re-appearance" to "reappearance" on page 159: "reappearance of the sun." Changed question 20 to "29" on page 174 to maintain proper sequence. Changed "proportionably" to "proportionally" on page 198: "proportionally distinct." Inserted comma after "Circle" on page 206 in the glossary entry for "Circle, Lesser." Inserted period on page 207 at the end of the glossary entry for "Cylinder." Changed "musisical" to "musical" on page 208 in the glossary entry for "Harmony." Changed "perpendidicular" to "perpendicular" on page 211: "perpendicular to each other."