# Reference image credits

Reference images of famous engineering sketches and patent drawings for the Napkin promo video. All files were resized to at most 2400 px on the long edge and converted to PNG. Patent PDFs were rendered at 300 dpi, and only the named drawing sheet was kept.

| File | What it shows | Year | Source | License / status | Attribution required |
|---|---|---|---|---|---|
| `davinci-codex-atlanticus-machines.png` | Leonardo da Vinci, Codex Atlanticus f. 1069 recto: pen sketches of water-raising machines, gear trains and pumps | c. 1482 | https://commons.wikimedia.org/wiki/File:Codex_Atlanticus_f1069_recto.png (original: Biblioteca Ambrosiana) | Public domain (PD-Art via Wikimedia Commons) | None. Suggested credit: "Leonardo da Vinci, Codex Atlanticus f. 1069r, Biblioteca Ambrosiana" |
| `watt-steam-engine-condenser.png` | Boulton & Watt double-acting engine (1784 design): beam, separate condenser and air pump, sun-and-planet gear, governor | Drawing published 1878 | https://commons.wikimedia.org/wiki/File:SteamEngine_Boulton%26Watt_1784.png (from R. H. Thurston, *A History of the Growth of the Steam-Engine*, 1878) | Public domain (PD-old) | None. Suggested credit: "R. H. Thurston, 1878" |
| `bell-telephone-notebook.png` | Alexander Graham Bell's lab notebook, pp. 40–41, March 10, 1876: liquid transmitter sketch and the "Mr. Watson — Come here" entry | 1876 | https://commons.wikimedia.org/wiki/File:AGBell_Notebook.jpg (Alexander Graham Bell Family Papers, Library of Congress) | Public domain (PD-old) | None. Suggested credit: "Library of Congress, Manuscript Division" |
| `edison-electric-lamp-patent.png` | T. A. Edison, US 223,898 "Electric-Lamp", drawing sheet (carbon filament bulb) | 1880 | https://commons.wikimedia.org/wiki/File:Drawing_for_an_Electric_Lamp_-_NARA_-_595450.jpg (US National Archives, NAID 595450) | Public domain (US patent, NARA record) | None. Suggested credit: "U.S. National Archives" |
| `tesla-induction-motor-patent.png` | N. Tesla, US 381,968 "Electro-Magnetic Motor", sheet 1 (rotating magnetic field figures) | 1888 | https://patents.google.com/patent/US381968A/en | Public domain (US patent) | None |
| `wright-flyer-patent.png` | O. & W. Wright, US 821,393 "Flying-Machine", sheet 1 (wing structure with wing-warping) | 1906 | https://patents.google.com/patent/US821393A/en | Public domain (US patent) | None |
| `goddard-rocket-patent.png` | R. H. Goddard, US 1,102,653 "Rocket Apparatus", sheet 1 (multi-stage rocket) | 1914 | https://patents.google.com/patent/US1102653A/en | Public domain (US patent) | None |
| `whittle-turbojet-patent.png` | F. Whittle, US 2,168,726 "Propulsion of Aircraft and Gas Turbines", sheet 1 (turbojet cross-section). Used in place of GB 347,206 (see below) | 1939 (filed 1937) | https://patents.google.com/patent/US2168726A/en | Public domain (US patent) | None |
| `lamarr-antheil-frequency-hopping-patent.png` | H. K. Markey (Hedy Lamarr) & G. Antheil, US 2,292,387 "Secret Communication System", sheet 1 | 1942 | https://patents.google.com/patent/US2292387A/en | Public domain (US patent) | None |
| `de-mestral-velcro-patent.png` | G. de Mestral, US 2,717,437 "Velvet Type Fabric and Method of Producing Same" (hook-and-loop) | 1955 | https://patents.google.com/patent/US2717437A/en | Public domain (US patent) | None. "Velcro" is a trademark; avoid implying endorsement |
| `fuller-geodesic-dome-patent.png` | R. B. Fuller, US 2,682,235 "Building Construction", sheet 1 (geodesic dome) | 1954 | https://patents.google.com/patent/US2682235A/en | Public domain (US patent) | None |
| `kilby-integrated-circuit-patent.png` | J. S. Kilby, US 3,138,743 "Miniaturized Electronic Circuits", sheet 2 (Fig. 6a/6b: the flying-wire IC and its equivalent circuit). The drawing is sideways on the sheet, as published | 1964 (filed 1959) | https://patents.google.com/patent/US3138743A/en | Public domain (US patent) | None |
| `engelbart-mouse-patent.png` | D. C. Engelbart, US 3,541,541 "X-Y Position Indicator for a Display System", sheet 1 (the mouse) | 1970 | https://patents.google.com/patent/US3541541A/en | Public domain (US patent) | None |
| `dyson-cyclone-vacuum-patent.png` | J. Dyson, US 4,593,429 "Vacuum Cleaning Appliance", sheet 1 (upright cleaner with cyclone and airflow arrows) | 1986 (filed 1984) | https://patents.google.com/patent/US4593429A/en | Public domain (US patent) | None. "Dyson" is a trademark; avoid implying endorsement |

Note on US patents: US patent text and drawings are generally not subject to copyright (37 CFR 1.71, USPTO policy). Trademarks that appear in them (Velcro, Dyson) are still protected, so don't use them in a way that suggests endorsement.

## Substitutions and skips

- **James Watt (1769 patent):** GB patent No. 913 (1769) has no drawings; it is text only (checked on https://commons.wikimedia.org/wiki/File:James_Watt_Patent_1769_No_913.pdf). No public-domain scan of Watt's own condenser sketch was found on Commons, so a public-domain 1878 engraving of the Boulton & Watt engine is used instead. A more period-accurate alternative is the plate in *Encyclopaedia Britannica*, 3rd ed. (1797): https://commons.wikimedia.org/wiki/File:WattsSteamEngine.jpeg. That scan is tagged CC BY-SA 3.0 (credit "DigbyDalton"), so it was not used because of the share-alike terms.
- **Frank Whittle, GB 347,206 (1930/1931):** Google Patents has no page images for it, and Commons has no free copy. UK patent documents are not automatically public domain, and Whittle died in 1996. His US patent 2,168,726 (filed 1937), which shows the same turbojet concept, is used instead. The Commons "Whittle W.1X Turbojet Engine" files (CC0) are museum photos, not drawings, so they were not used.
- **Robert Goddard:** No public-domain scan of the 1926 liquid-fuel rocket sketch was found on Commons, so the 1914 patent drawing is used. US 1,103,503 (1914, which covers liquid propellants) is also public domain at https://patents.google.com/patent/US1103503A/en, but its sheet 1 is much busier and harder to read on video.
- **Jack Kilby notebook (1958):** The original is held by Texas Instruments and no public-domain or free-licensed scan was found, so the patent drawing is used.
- **Leonardo da Vinci flying machine:** The free Commons copies of the ornithopter folio (Ms. B) are only about 500 px, too small for video, so the high-resolution Codex Atlanticus mechanism sheet is used.
- **Tim Berners-Lee, "Information Management: A Proposal" (1989): SKIPPED.** The document and its diagram are CERN material. No clear free license was found, and CERN's 1993 public-domain release covered the web software, not this proposal. Commons has no free-licensed copy. To use it, get permission from CERN or present it as a brief quotation under fair use, after legal review.