may provide "certain activities, which gradually accumulate meaning until they become homes". Joseph Rykwert distinguished between home and house in their physicality; a house requires a building whereas a home does not. Home and house are often used interchangeably, although their connotations may differ: house being "emotionally netural" and home evoking "personal, cognitive aspects". By the mid-18th century, the definition of home had extended beyond a house. "Few English words are filled with the emotional meaning of the word home". Moveable structures Home as constitutionally mobile and transient has been contended by anthropologists and sociologist. A mobile home (also known as a house trailer, park home, trailer, or trailer home) is a prefabricated structure, built in a factory on a permanently attached chassis before being transported to site (either by being towed or on a trailer). Used as permanent homes, or for holiday or temporary accommodation, they are often left permanently or semi-permanently in one place, but can be moved, and may be required to move from time to time for legal reasons. A houseboat is a boat that has been designed or modified to be used primarily as a home. Some houseboats are not motorized, because they are usually moored, kept stationary at a fixed point and often tethered to land to provide utilities. However, many are capable of operation under their own power. Float house is a Canadian and American term for a house on a float (raft); a rough house may be called a shanty boat. In Western countries, houseboats tend to be either owned privately or rented out to holiday-goers, and on some canals in Europe, people dwell in houseboats all year round. Examples of this include, but are not limited to, Amsterdam, London, and Paris. A traditional yurt or ger is a portable round tent covered with skins or felt and used as a dwelling by several distinct nomadic groups in the steppes of Central Asia. The structure consists of an angled assembly or latticework of wood or bamboo for walls, a door frame, ribs (poles, rafters), and a wheel (crown, compression ring) possibly steam-bent. The roof structure is often self-supporting, but large yurts may have interior posts supporting the crown. The top of the wall of self-supporting yurts is prevented from spreading by means of a tension band which opposes the force of the roof ribs. Modern yurts may be permanently built on a