Used to be, waiting until the last minute to book a summer trip could yield substantial savings. These days that's a risky move. Airlines in the U.S. and Europe cut back on capacity when fuel costs were high last year. Oil prices have fallen, but with the recession dampening travel demand, airlines continue to fly smaller and fewer planes. That means the cheapest seats fill up fast. So book your flight this month.

Sign up for low-fare e-mail alerts at FareCompare.com or Airfarewatchdog.com, which combs through airline websites for unpublished sales. In February, Airfarewatchdog noted that US Airways was offering roundtrip flights to Paris from many U.S. hubs for about $600, compared with an average of about $1,000. Such sales are fleeting - this one lasted two days - so be ready to jump.

Travel packagers and hotels are also offering breaks to those who buy in advance. Trafalgar Tours is discounting the airfare part of its peak-season packages to six European destinations by 56% for those who pay by March. At the luxury Fairmont chain, which has six hotels in Europe, guests who pay three weeks in advance get 30% or more off the best available rates - as low as $138 a night at the Fairmont in St. Andrews, Scotland.

Bottom line: The early booker gets the deal. "If you wait past April, you'll need to be flexible on where and when you go to save," says SmarterTravel's Banas.

But if you can't book by April ... reduce costs by looking for flights with one or more stops. On United, for example, midsummer roundtrips to Paris are about $1,000 nonstop, but as low as $614 if you connect through Frankfurt. Or fly a non-European carrier that stops in Europe. Going with Air Tahiti, which stops in Paris on its way from Los Angeles to Tahiti, can knock several hundred bucks off the fare.

In its early stages of development, television employed a combination of optical, mechanical and electronic technologies to capture, transmit and display a visual image. By the late 1920s, however, those employing only optical and electronic technologies were being explored. All modern television systems rely on the latter, although the knowledge gained from the work on mechanical-dependent systems was crucial in the development of fully electronic television.

The first time images were transmitted electrically were via early mechanical fax machines, including the pantelegraph, developed in the late 1800s. The concept of electrically-powered transmission of television images in motion, was first sketched in 1878 as the telephonoscope, shortly after the invention of the telephone. At the time, it was imagined by early science fiction authors, that someday that light could be transmitted over wires, as sounds were.

The idea of using scanning to transmit images was put to actual practical use in 1881 in the pantelegraph, through the use of a pendulum-based scanning mechanism. From this period forward, scanning in one form or another, has been used in nearly every image transmission technology to date, including television. This is the concept of "rasterization", the process of converting a visual image into a stream of electrical pulses.

Linguistics is the scientific study of natural language. Linguistics encompasses a number of sub-fields. An important topical division is between the study of language structure (grammar) and the study of meaning (semantics). Grammar encompasses morphology (the formation and composition of words), syntax (the rules that determine how words combine into phrases and sentences) and phonology (the study of sound systems and abstract sound units). Phonetics is a related branch of linguistics concerned with the actual properties of speech sounds (phones), non-speech sounds, and how they are produced and perceived. Other sub-disciplines of linguistics include the following: evolutionary linguistics, which considers the origins of language; historical linguistics, which explores language change; sociolinguistics, which looks at the relation between linguistic variation and social structures; psycholinguistics, which explores the representation and functioning of language in the mind; neurolinguistics, which looks at the representation of language in the brain; language acquisition, which considers how children acquire their first language and how children and adults acquire and learn their second and subsequent languages; and discourse analysis, which is concerned with the structure of texts and conversations, and pragmatics with how meaning is transmitted based on a combination of linguistic competence, non-linguistic knowledge, and the context of the speech act.

Linguistics is narrowly defined as the scientific approach to the study of language, but language can, of course, be approached from a variety of directions, and a number of other intellectual disciplines are relevant to it and influence its study. Semiotics, for example, is a related field concerned with the general study of signs and symbols both in language and outside of it. Literary theorists study the use of language in artistic literature. Linguistics additionally draws on work from such diverse fields as psychology, speech-language pathology, informatics, computer science, philosophy, biology, human anatomy, neuroscience, sociology, anthropology, and acoustics.

Within the field, linguist is used to describe someone who either studies the field or uses linguistic methodologies to study groups of languages or particular languages. Outside the field, this term is commonly used to refer to people who speak many languages or have a great vocabulary.

Auroras are produced by the collision of charged particles from Earth's magnetosphere, mostly electrons but also protons and heavier particles, with atoms and molecules of Earth's upper atmosphere (at altitudes above 80 km (50 miles)). The particles have energies of 1 to 100 keV. They originate from the Sun and arrive at the vicinity of Earth in the relatively low-energy solar wind. When the trapped magnetic field of the solar wind is favorably oriented (principally southwards) it connects with Earth's magnetic field, and solar particles enter the magnetosphere and are swept to the magnetotail. Further magnetic reconnection accelerates the particles towards Earth.

The collisions in the atmosphere electrically excite electrons to take quantum leaps (a mechanism in which the electron's kinetic energy is converted to visible light); and molecules in the upper atmosphere. The excitation energy can be lost by light emission or collisions. Most auroras are green and red emissions from atomic oxygen. Molecular nitrogen and nitrogen ions produce some low level red (pink) and very high blue/violet auroras. The light blue and green colors are produced by ionic nitrogen and the neutral helium gives off the purple colour whereas neon is responsible for the rare orange flares with the rippled edges. Different gasses interacting with the upper atmosphere will produce different colors, caused by the different compounds of oxygen and nitrogen. The level of solar wind activity from the Sun can also influence the color and intensity of the auroras.

The Birkin bag is a handbag manufactured by leather goods and ready-to-wear manufacturer Hermès. It is named after British-born actress and singer Jane Birkin, a longtime resident of France.

Press accounts of the bag's genesis differ in details. Birkin told noted fashion writer Dana Thomas that while seated next to Hermès CEO Jean-Louis Dumas in 1984 on a Paris to London flight, she opened her Hermès-made datebook and a flurry of loose notes fell to the floor. Dumas took her datebook and returned it a few weeks later with a pocket sewn into the back (which has since become standard). Birkin went on to discuss with Dumas her difficulty in finding a leather weekend bag and at his prompting, described her ideal. Shortly thereafter, the bag she described arrived at her flat with a note from Dumas.

A more piquant version of the story was repeated by film director Andrew Litvack. He put the year as 1981 and says that Birkin was called to Hermès to receive the first prototype. As she was leaving with the bag, they asked if she had forgotten something. Puzzled, she realized they wanted her to pay for it. Litvack claims Birkin was eventually reimbursed, and now receives a 10% discount on Hermès products.

PageRank is a link analysis algorithm, named after Larry Page, used by the Google Internet search engine that assigns a numerical weighting to each element of a hyperlinked set of documents, such as the World Wide Web, with the purpose of "measuring" its relative importance within the set. The algorithm may be applied to any collection of entities with reciprocal quotations and references. The numerical weight that it assigns to any given element E is also called the PageRank of E and denoted by PR(E).

Google describes PageRank, "PageRank relies on the uniquely democratic nature of the web by using its vast link structure as an indicator of an individual page's value. In essence, Google interprets a link from page A to page B as a vote, by page A, for page B. But, Google looks at more than the sheer volume of votes, or links a page receives; it also analyzes the page that casts the vote. Votes cast by pages that are themselves "important" weigh more heavily and help to make other pages "important"."

In other words, a PageRank results from a "ballot" among all the other pages on the World Wide Web about how important a page is. A hyperlink to a page counts as a vote of support. The PageRank of a page is defined recursively and depends on the number and PageRank metric of all pages that link to it ("incoming links"). A page that is linked to by many pages with high PageRank receives a high rank itself. If there are no links to a web page there is no support for that page.

PageRank is a link analysis algorithm, named after Larry Page, used by the Google Internet search engine that assigns a numerical weighting to each element of a hyperlinked set of documents, such as the World Wide Web, with the purpose of "measuring" its relative importance within the set. The algorithm may be applied to any collection of entities with reciprocal quotations and references. The numerical weight that it assigns to any given element E is also called the PageRank of E and denoted by PR(E).

Google describes PageRank, "PageRank relies on the uniquely democratic nature of the web by using its vast link structure as an indicator of an individual page's value. In essence, Google interprets a link from page A to page B as a vote, by page A, for page B. But, Google looks at more than the sheer volume of votes, or links a page receives; it also analyzes the page that casts the vote. Votes cast by pages that are themselves "important" weigh more heavily and help to make other pages "important"."

In other words, a PageRank results from a "ballot" among all the other pages on the World Wide Web about how important a page is. A hyperlink to a page counts as a vote of support. The PageRank of a page is defined recursively and depends on the number and PageRank metric of all pages that link to it ("incoming links"). A page that is linked to by many pages with high PageRank receives a high rank itself. If there are no links to a web page there is no support for that page.

Electronic mail, often abbreviated as email or e-mail, is a method of exchanging digital messages, designed primarily for human use. E-mail systems are based on a dstore-and-forward model in which e-mail computer server systems accept, forward, deliver and store messages on behalf of users, who only need to connect to the e-mail infrastructure, typically an e-mail server, with a network-enabled device (e.g., a personal computer) for the duration of message submission or retrieval. Rarely is e-mail transmitted directly from one user's device to another's.

An electronic mail message consists of two components, the message header, and the message body, which is the email's content. The message header contains control information, including, minimally, an originator's email address and one or more recipient addresses. Usually additional information is added, such as a subject header field.

Originally a text-only communications medium, email is extended to carry multi-media content attachments, which were standardized in with RFC 2045 through RFC 2049, collectively called, Multipurpose Internet Mail Extensions (MIME).

The foundation for today's global Internet e-mail service was created in the early ARPANET and standards for encoding of messages were proposed as early as, for example, in 1973 (RFC 561). An e-mail sent in the early 1970s looked very similar to one sent on the Internet today. Conversion from the ARPANET to the Internet in the early 1980s produced the core of the current service.

Network-based email was initially exchanged on the ARPANET in extensions to the File Transfer Protocol (FTP), but is today carried by the Simple Mail Transfer Protocol (SMTP), first published as Internet Standard 10 (RFC 821) in 1982. In the process of transporting email messages between systems, SMTP communicates delivery parameters using a message envelope separately from the message (headers and body) itself.