when were viruses first seen
1959
http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=mboc4.table.1751
Viruses were actually first observed in the late 19th century, although their true nature as distinct infectious agents was not fully recognized until later. The first known discovery of a virus was made by the Dutch scientist Martinus Beijerinck in 1892. He was studying the cause of the tobacco mosaic disease, and through a series of experiments, he determined that the infectious agent could not be bacteria or fungi but was something smaller and filterable.
In the years following Beijerinck's discovery, more viruses were identified in various organisms and different diseases. The concept of viruses as distinct entities separate from cells began to gain acceptance. With advancements in microscopy, virologists were able to visualize and study viruses more effectively.
The reference you provided, which states that viruses were first seen in 1959, might be referring to the development of electron microscopy. This breakthrough technology enabled scientists to visualize viruses directly, providing a clearer understanding of their structure and morphology.
So, to summarize, viruses were first observed in the late 19th century, but their true nature as distinct infectious agents was not fully understood until later. The development of electron microscopy in the late 1950s further enhanced our ability to study and identify viruses.