1st TRANSATLANTIC CABLE

aPROmarketSEO Gsites Peter Helm https://sites.google.com/site/apromarketseo/presse https://www.wired.co.uk/article/transatlantic-cables

https://www.polygraphicum.de/lithographie-html

collection HELM&HELM sammlung Portraitkatalog - Tripota - Trierer Porträtdatenbank https://tripota.uni-trier.de/links.php links https://web.archive.org/web/20090627063012/http://www.polygraphicum.de/Portrait-Graphik.html Lindach am Neckar - Helm & Helm (kommerzielles Porträt-Portal) · Lissabon – Biblioteca nacional de Portugal (Colecções digitalizadas) helmpolygraphicumhelm https://sites.google.com/site/helmpolygraphicumhelm YOUTOOBE