Led by Oxford graduate Duncan Greatwood, Topsy provides access to the "firehose" of every tweet generated on Twitter, and also indexes social networks including Facebook and Google+.
The purchase follows the acquisition at the end of last month of PrimeSense, an Israeli technology company, for around $350m.
But the new addition suggests that Apple is seeking to expand its influence in the social media sphere - an area where it has previously struggled to make any impact after the failure of its Ping social music service, which chief executive Tim Cook shut down in September 2012.
An Apple spokesperson confirmed the purchase to the Guardian, saying "Apple buys smaller technology companies from time to time, and we generally do not discuss our purpose or plans."
Apple's purpose in buying the company could be to improve its iAds service, which has suffered from poor sales, or to improve its general web services functionality as it tries to compete with Google and Microsoft as the basis of smartphone and tablet competition shifts from hardware towards software and services. Apple lags behind Google in particular in web services, where the search company has advantages in fields such as local data, maps, and voice search.
Alternatively it may intend to use it for indexing apps and to improve search using its Siri voice control system and in the App Store, where finding the right app is increasingly difficult as the catalogue grows.
Topsy, founded in 2007, has created a complete searchable archive of 450 billion tweets sent over Twitter since it was set up, and added other analytics tools to make itself useful to businesses - who can buy pro services in order to tailor their social efforts
The company had raised a total of $35m in venture capital up to September. Vipul Ved Prakash, the co-founder and chief technology officer, told Techcrunch in September that “The amount of data being created on Twitter plus Facebook today is more than the data being created on the rest of the web… Social data has become the bigger public corpus.”
Prakash said then that the company had built indexes which could be applied to Facebook, and that it had archived every public Google+ post.
Topsy's essential power is seen as being able to evaluate "sentiment" around tweets and in peoples' comments on social networks.
• Apple bought PrimeSense - hose technology was in the first Kinect - with a clear intentionThis article was written by Charles Arthur, for theguardian.com on Monday 2nd December 2013 23.17 Europe/London
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