![]() ![]() A formula similar to oak gall ink was created by James Jay and used by George Washington and the Culper Spy Ring during the American Revolution and lemon juice was used by the 'Lemon Juice Spies' (Carl Muller and 4 other Germans, who all died for their efforts either by suicide or execution, along with John Hahn, an English baker) during World War I. : 24 Since then, a wide variety of invisible inks have been used for all sorts of secretive purposes. Giovanni Battista della Porta is credited with the first recipe for a sympathetic ink, derived from alum and vinegar, as well as the first book on secret writing and invisible inks, Magia Naturalis(1558, 1589). Lemons were also used as organic inks by Arabs around 600 AD, and during the 16th century in Europe. ![]() Pliny the Elder and the Roman poet Ovid gave advice on the use of plant juices and milk to write secret messages. People soon discovered that they could write invisibly with one of the ingredients and then cause the writing to appear by adding the other. These ingredients were used to make oak gall ink. Philo of Byzantium may be the first writer known to describe an invisible ink using a reagent around 217–218 BC, with oak galls and vitriol. They used invisible ink and microdots instead of pinpricks. This did not include an invisible ink but the Germans improved on the method during World War I and World War II. One of the techniques that involved steganography involved puncturing a tiny hole above or below letters in a document to spell out a secret message. This was part of his list of the 20 different methods of secret communications in a book called On the Defense of Fortifications. He mentions it in discussing how to survive under siege but does not indicate the type of ink to be used. One of the earliest writers to mention an invisible ink is Aeneas Tacticus, in the 4th century BC. Invisible ink is one form of steganography. ![]() Invisible ink, also known as security ink or sympathetic ink, is a substance used for writing, which is invisible either on application or soon thereafter, and can later be made visible by some means, such as heat or ultraviolet light. Handwriting by Peggy Shippen Arnold is interspersed with coded communication in Arnold's hand. ![]() JSTOR ( January 2020) ( Learn how and when to remove this template message)Ī coded letter from Benedict Arnold, originally written in invisible ink.Unsourced material may be challenged and removed. Please help improve this article by adding citations to reliable sources. Though all readers allow you to side-load unprotected content, it’s important that they provide easy access to a large library of commercial books.This article needs additional citations for verification. Library: Ebook readers can’t stand on the strength of their hardware alone.Other features: Features like waterproofing and Bluetooth audio can make a good e-reader great, but they’re not required.Because e-readers tend to be so similar in this regard, specs like these are less important than how good an ebook reader feels in the hand. Battery life and storage: Most e-readers promise battery life somewhere between six and eight weeks, depending on usage, and offer 8 GB or 32 GB of storage.Newer e-readers pack larger screens into similarly sized bodies, which is a bonus. The most common screen size is 6 inches, which is also the most portable. Build quality and size: While most ebook readers are made of plastic, some feel better than others in your hands.Anything lower produces less-crisp text and images. Screen quality: We gave preference to devices with a pixel density of 300 dots per inch, the highest available in any ebook reader and what most models offer.Because this feature is so prevalent, we didn’t test any readers without it. Unlike tablets such as the iPad, ebook readers use a side-lighting system that provides a glow across the screen, rather than from behind it. Built-in lighting: Most e-readers provide their own light for reading in dark environments. ![]()
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