| Maclean, John |
0014, 0017 |
| Maclure, William |
0063, 0073, 0106, 0125, 0209 |
| Mall, Franklin Paine |
0772, 0927 |
| Mansfield, Jared |
0031 |
| Marcou, Jules |
0315, 0344 |
| Marine Biological Laboratory (Woods Hole, Mass.) |
0620, 0744 |
| Markoe, Francis, Jr. |
0241 |
| Marsh, George Perkins |
0384 |
| Marsh, Othniel Charles |
0397, 0469, 0503, 0532, 0542 |
| Martin, Henry Newell |
0550, 0603 |
| Massachusetts General Hospital |
0256 |
| Massachusetts geological and natural history survey |
0189, 0218 |
| Massachusetts Institute of Technology |
0366, 0412, 0465, 0512 |
| Massachusetts Society for Promoting Agriculture |
0006 |
| Massachusetts state board of health |
0418 |
| Mathematical Association of America |
0695 |
| Mathematical Correspondent |
0048 |
| Mathematical Diary |
0128 |
| Mather, William Williams |
0184, 0193 |
| Maury, Antonia |
0710 |
| Maury, Matthew Fontaine |
0153, 0222, 0259, 0288, 0316, 0331, 0463 |
| Mayer, Alfred Marshall |
0515 |
| McClung, Clarence Erwin |
0779 |
| McCormick, Cyrus |
0163 |
| McDowell, Ephraim |
0064 |
| McLean Hospital for the Insane |
0755 |
| McMahon, Bernard |
0054 |
| Medical Repository |
0018 |
| Meek, Fielding Bradford |
0340 |
| Melsheimer, Frederick V. |
0056 |
| Mendel, Lafayette Benedict |
0826 |
| Mergenthaler, Ottmar |
0580 |
| Merriam, Clinton Hart |
0591, 0643, 0739 |
| Merrill, George Perkins |
0157, 0661, 0724 |
| Metallographist |
0735 |
| Metaphysical Club |
0436 |
| Michael, Arthur |
0522 |
| Michaux, Andre |
0043 |
| Michaux, Francois A. |
0043, 0230 |
| Michelson, Albert Abraham |
0516, 0607, 0805, 0858 |
| Miller, Dayton Clarence |
0797, 0886 |
| Miller, George Abram |
0751 |
| Miller, Samuel |
0044 |
| Millikan, Robert A. |
0922 |
| Minot, Charles Sedgwick |
0574, 0596, 0679, 0772 |
| Missouri Botanical Garden |
0350 |
| Mitchel, Ormsby MacKnight |
0225, 0253 |
| Mitchell, Maria |
0266, 0275 |
| Mitchell, Silas Weir |
0450 |
| Mitchill, Samuel Latham |
0010, 0017, 0018, 0020, 0023, 0094 |
| Monist |
0649.5 |
| Monsanto corporation |
0770 |
| Montgomery, Edmund Duncan |
0810 |
| Montgomery, Thomas Harrison, Jr. |
0765 |
| Monthly American Journal of Geology and Natural Science |
0162 |
| Morehouse, George R. |
0450 |
| Morgan, Lewis Henry |
0496 |
| Morgan, Thomas Hunt |
0909 |
| Morley, Edward W. |
0607, 0797 |
| Morrill Act (federal land-grant college bill) |
0374 |
| Morse, Edward Sylvester |
0385, 0408, 0505 |
| Morse, Samuel F.B. |
0192, 0223, 0242 |
| Morton, Samuel George |
0177, 0204 |
| Morton, William Thomas Green |
0256 |
| Moulton, Forest Ray |
0829 |
| Mount Wilson Observatory |
0815, 0875 |
| Muhlenberg, Gotthilf Henry Ernest |
0076, 0084 |
| Muir, John |
0654 |
| Munn, Orson |
0247 |
| Myer, Albert J. |
0430 |
